Organic semiconductor polymer, composition for organic semiconductor material, and photovoltaic cell

ABSTRACT

An organic semiconductor polymer having a structural unit represented by the following Formula (I), a composition for organic semiconductor material, a photovoltaic cell and a polymer. 
     
       
         
         
             
             
         
       
         
         
           
             wherein X represents Si, S or O; R 1  represents a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, an aromatic heterocyclic group or an oxygen atom; p represents 0, 1 or 2; herein, the bond between X and R 1  is such that when X is Si, the bond is a single bond, and when X is S, the bond is a double bond. Furthermore, when X is O, p represents 0.

TECHNICAL FIELD

The present invention relates to an organic semiconductor polymer, acomposition for organic semiconductor material and a photovoltaic cell.

BACKGROUND ART

Organic semiconductor polymers have been a subject of active research inrecent years in the field of organic electronics, and the polymers areused in organic electroluminescent elements that emit light whenelectricity is passed, organic photoelectric conversion elements thatgenerate power when irradiated with light, organic thin film transistorelements that control the amount of current or the amount of voltage,and the like. In such an element, similarly to an inorganicsemiconductor material, use is made of an organic semiconductor materialobtained by combining a p-type conductive semiconductor material, whichis an electron donor material, and an n-type conductive semiconductormaterial, which is an electron acceptor material.

In recent years, since fossil energy of petroleum and the like emitcarbon dioxide to the atmosphere, for the purpose of global environmentpreservation with the suppression of global warming, there is anincreasing demand of solar cells. Known examples of organic solar cellsthat use organic photoelectric conversion elements include a wet typedye-sensitized solar cell (Gräetzel cell) and a total solid type organicthin film solar cell. Since the latter does not use an electrolytesolution, there is no need to take evaporation of this electrolytesolution or liquid leakage into consideration, the solar cell can bemade flexible, and the structure of the solar cell or production thereofis more convenient than that of the former.

However, the photoelectric conversion efficiency of organic thin filmsolar cells is still insufficient. The photoelectric conversionefficiency is calculated by short circuit current (Jsc)×open circuitvoltage (Voc)×fill factor (FF); according to which, in order to increasethis efficiency, an increase in the open circuit voltage is also neededalong with an increase in the short circuit current. The short circuitcurrent is increased when an organic semiconductor material having highsolubility and carrier mobility (for example, a compound having afluorene structure or a silafluorene structure) is used. The opencircuit voltage, which is said to be connected with the differencebetween the HOMO energy level of the p-type conductive semiconductormaterial and the LUMO energy level of the n-type conductivesemiconductor material, is raised when this difference is increased.Furthermore, in the case of an organic solar cell, in order to increasethe efficiency, it is efficient to absorb more light of a region oflonger wavelengths (650 nm to 800 nm) than the wavelengths of sunlight.Therefore, band gap narrowing is desirable. It is expected that theenhancement of luminescence efficiency, that is, enhancement of thepower efficiency of organic electroluminescent lighting for an organicelectroluminescent element.

On the other hand, studies on organic semiconductor polymers as p-typeconductive semiconductor materials, which are electron donor materials,are in active progress. For example, Patent Literature 1 suggests apolymer having a particular cyclopentadithiazole structure, and PatentLiterature 2 suggests a polymer having a particularsilacyclopentadithiophene structure. However, in both cases, theconversion efficiency of the solar cell using the above-mentionedpolymers is not necessarily sufficient, and these polymers are notsatisfactory in terms of durability, and particularly in terms ofdurability in the presence of oxygen.

CITATION LIST Patent Literatures

-   Patent Literature 1: WO 08/067,023-   Patent Literature 2: JP-T-2010-507233 (“JP-T” means searched and    published

SUMMARY OF THE INVENTION Technical Problem

An object of the present invention is to provide an organicsemiconductor polymer which has excellent photoelectric conversionefficiency and is excellent in durability, and particularly indurability in the presence of oxygen, and which has a smaller decreasein the photoelectric conversion efficiency even in the case where thecell size is increased. Particularly, it is an object of the presentinvention to achieve a good balance between band gap narrowing conductedto enhance the photoelectric conversion efficiency and an enhancement ofdurability, and then to provide an organic semiconductor polymer whichhas a reduced cell size-dependency of the photoelectric conversionefficiency. Furthermore, another object of the present invention is toprovide a composition for organic semiconductor materials containingsuch an organic semiconductor polymer, and a photovoltaic cell(particularly, an organic thin film solar cell) having the polymer orthe composition. Moreover, still another object of the present inventionis to provide a polymer which is useful for organic electronic devicessuch as an organic electroluminescent element and an organic thin filmtransistor element.

Solution to Problem

The inventors of the present invention conducted thorough investigationsin order to achieve the problems described above, and as a result, theypaid attention to the deep HOMO energy level of organic semiconductorpolymers for an enhancement in the efficiency of organic semiconductorpolymers, particularly an enhancement in durability, and investigatedvarious compounds having such a polymer structure. Thereby, theinventors found that an organic semiconductor polymer having aparticular structure can achieve a balance between wavelengthlengthening of the absorption wavelength in the band gap narrowing of aphotovoltaic cell, and an enhancement of durability. Particularly, for agood balance between the photoelectric conversion efficiency anddurability, the condensation arrangement and the kind of three rings areimportant, and when the thiazole structure is linked to a particularelement, the HOMO energy level can be made deeper. Also, in regard tothe prevention of a decrease in the photoelectric conversion efficiencyby the dependency on cell size, although it is not clearly known, it isthought that by adopting the relevant structure of the invention, theπ-π stacking properties between polymer molecules are enhanced, and itis made easier to adopt a molecular arrangement that is preferable for awide cell area. As a result, it was found that efficient batterycharacteristics are exhibited in a wide region.

The present invention has been achieved based on those finding.

All of the problems of the present invention can be solved by thefollowing means.

<1> An organic semiconductor polymer having a structural unitrepresented by the following Formula (I):

wherein X represents Si, S or O; R¹ represents a hydrogen atom, an alkylgroup, a cycloalkyl group, an aryl group, an aromatic heterocyclic groupor an oxygen atom; p represents 0, 1 or 2; herein, the bond between Xand R¹ is such that when X is Si, the bond is a single bond, and when Xis S, the bond is a double bond. Furthermore, when X is O, p represents0, and when p is 2, two R¹'s may be the same or different from eachother, or two R¹'s may bond with each other to form a ring.

<2> The organic semiconductor polymer described in the above item <1>,wherein the structural unit represented by Formula (I) is a structuralunit represented by Formula (I-1):

wherein R¹′ and R¹″ each independently represent a hydrogen atom, analkyl group, a cycloalkyl group, an aryl group or an aromaticheterocyclic group; and R¹′ and R¹″ may bond with each other to form aring.

<3> The organic semiconductor polymer described in the above item <1>,wherein the structural unit represented by Formula (I) is a structuralunit represented by Formula (I-2):

wherein p′ represents 0, 1 or 2.

<4> The organic semiconductor polymer described in the above item <1>,wherein the structural unit represented by Formula (I) is a structuralunit represented by Formula (I-3):

<5> The organic semiconductor polymer described in any one of the aboveitems <1> to <4>, wherein the organic semiconductor polymer is aco-polymer.<6> The organic semiconductor polymer described in any one of the aboveitems <1> to <4>, wherein the organic semiconductor polymer is aco-polymer which further includes a structural unit represented by thefollowing Formula (II):

wherein Z¹ and Z² each independently represent S, O, Se or Te; Yrepresents C(R²¹) or N; R and R²¹ each independently represent ahydrogen atom or a substituent.

<7> A composition for organic semiconductor material, including theorganic semiconductor polymer described in any one of the above items<1> to <6> and an n-type organic semiconductor molecule.<8> The composition for organic semiconductor material described in theabove item <7>, wherein the n-type organic semiconductor molecule isfullerene or a derivative thereof.<9> The composition for organic semiconductor material described in theabove item <8>, wherein the fullerene or a derivative thereof is aphenyl-C₆₁-butyric acid ester, a diphenyl-C₆₂-bis(butyric acid ester), aphenyl-C₇₁-butyric acid ester, a phenyl-C₈₅-butyric acid ester, or athienyl-C₆₁-butyric acid ester.<10> A photovoltaic cell including the organic semiconductor polymer orthe composition for organic semiconductor material described in any oneof the above items <1> to <9>.<11> A photovoltaic cell including a layer containing the organicsemiconductor polymer or the composition for organic semiconductormaterial described in any one of the above items <1> to <9>, between afirst electrode and a second electrode.<12> The photovoltaic cell described in the above item <11>, including ahole transport layer between the first electrode and the layercontaining the organic semiconductor polymer or the composition fororganic semiconductor material.<13> The photovoltaic cell described in the above item <11> or <12>,including an electron transport layer between the second electrode andthe layer containing the organic semiconductor polymer or thecomposition for organic semiconductor material.<14> The photovoltaic cell described in any one of the above items <11>to <13>, wherein the first electrode is a transparent electrode.<15> The photovoltaic cell described in any one of the above items <11>to <14>, wherein the second electrode is a metal electrode.<16> A polymer having a structural unit represented by the followingFormula (I):

wherein X represents Si, S or O; R¹ represents a hydrogen atom, an alkylgroup, a cycloalkyl group, an aryl group, an aromatic heterocyclic groupor an oxygen atom; p represents 0, 1 or 2; herein, the bond between Xand R¹ is such that when X is Si, the bond is a single bond, and when Xis S, the bond is a double bond. Furthermore, when X is O, p represents0, and when p is 2, two R¹'s may be the same or different from eachother, or two R¹'s may bond with each other to form a ring.

<17> The polymer described in the above item <16>, wherein thestructural unit represented by Formula (I) is a structural unitrepresented by Formula (I-1):

wherein R¹′ and R¹″ each independently represent a hydrogen atom, analkyl group, a cycloalkyl group, an aryl group or an aromaticheterocyclic group; and R¹′ and R¹″ may bond with each other to form aring.

<18> The polymer described in the above item <16>, wherein thestructural unit represented by Formula (I) is a structural unitrepresented by Formula (I-2):

wherein p′ represents 0, 1 or 2.

<19> The polymer described in the above item <16>, wherein thestructural unit represented by Formula (I) is a structural unitrepresented by Formula (I-3):

<20> The polymer described in any one of the above items <16> to <19>,wherein the polymer is a co-polymer.<21> The polymer described in any one of the above items <16> to <19>,wherein the polymer is a co-polymer which further includes a structuralunit represented by the following Formula (II):

wherein Z¹ and Z² each independently represent S, O, Se or Te; Yrepresents C(R²¹) or N; R and R²¹ each independently represent ahydrogen atom or a substituent.

Advantageous Effects of Invention

According to the present invention, an organic semiconductor polymerwhich has excellent photoelectric conversion efficiency and is excellentin durability, and particularly in durability in the presence of oxygen,and which has a smaller decrease in the photoelectric conversionefficiency even in the case where the cell size is increased; acomposition for organic semiconductor material containing the organicsemiconductor polymer; a photovoltaic cell (particularly, an organicthin film solar cell) including the polymer or the composition; and apolymer can be provided.

MODE FOR CARRYING OUT THE INVENTION

The inventors of the present invention paid attention to the HOMO energylevel of organic semiconductor polymers for an enhancement in theefficiency of organic semiconductor polymers, particularly anenhancement in durability, and investigated various compounds havingsuch a polymer structure. Thus, the inventors confirmed that the HOMOenergy level of an organic semiconductor polymer is related to Voc (opencircuit voltage) of a solar cell so that as this HOMO energy level islower, Voc increases, and also confirmed that although an organicsemiconductor polymer generally tends to be easily oxidized anddeteriorated, when the energy level is lowered, the stability tooxidation caused by oxygen in the atmosphere or the like is enhanced.The inventors then found that an organic semiconductor polymer having aparticular structure can achieve a balance between wavelengthlengthening of the absorption wavelength in the band gap narrowing of aphotovoltaic cell, and an enhancement of durability.

A photovoltaic cell containing the organic semiconductor polymer of thepresent invention has excellent photoelectric conversion efficiency andis excellent in durability, and particularly in durability in thepresence of oxygen, and even in the case where the cell size isincreased, the photovoltaic cell undergoes a small decrease in thephotoelectric conversion efficiency.

<Polymer Having Structure Unit Represented by Formula (I) of Invention>

First, the polymer having a structural unit represented by the followingFormula (I) of the present invention will be described.

In Formula (I), X represents Si, S or O; R¹ represents a hydrogen atom,an alkyl group, a cycloalkyl group, an aryl group, an aromaticheterocyclic group or an oxygen atom; p represents 0, 1 or 2; herein,the bond between X and R¹ is such that when X is Si, the bond is asingle bond, and when X is S, the bond is a double bond. Furthermore,when X is O, p represents 0, and when p is 2, two R¹'s may be the sameor different from each other, or two R¹'s may bond with each other toform a ring.

The polymer having a structural unit represented by the followingFormula (I) of the present invention will be described in detail below.

X represents Si, S or O. X is preferably Si or S, and more preferablySi. R¹ represents a hydrogen atom, an alkyl group, a cycloalkyl group,an aryl group, an aromatic heterocyclic group or an oxygen atom.

The alkyl group for R¹ is a substituted or unsubstituted, linear orbranched alkyl group, and preferably an alkyl group having 1 to 30carbon atoms. Examples thereof include methyl, ethyl, n-propyl,isopropyl, t-butyl, n-octyl, eicosyl, 2-chloroethyl, 2-cyanoethyl, and2-ethylhexyl.

The cycloalkyl group for R¹ is a substituted or unsubstituted cycloalkylgroup, and preferably a cycloalkyl group having 3 to 30 carbon atoms.Examples thereof include cyclohexyl, cyclopentyl, and4-n-dodecylcyclohexyl.

The aryl group for R¹ is a substituted or unsubstituted aryl group, andpreferably an aryl group having 6 to 30 carbon atoms. Examples thereofinclude phenyl, p-tolyl, naphthyl, m-chlorophenyl, and ano-hexadecanoylaminophenyl.

The aromatic heterocyclic group for R¹ is a substituted or unsubstitutedaromatic heterocyclic group, preferably having 0 to 30 carbon atoms, andpreferably being a 5-membered ring or a 6-membered ring. These rings maybe fused with an alicyclic ring, an aromatic ring, a heterocyclic ringand an aromatic heterocyclic ring. Examples of the heterocyclic ring forthe aromatic heterocyclic group include a furan ring, a pyrrole ring, apyridine ring, a thiophene ring, an imidazole ring, an oxazole ring, athiazole ring, a pyrazole ring, an isoxazole ring, an isothiazole ring,a pyrimidine ring, a pyrazine ring, a pyridazine ring, an indole ring,an indazole ring, a purine ring, and a quinoline ring.

The alkyl group, cycloalkyl group, aryl group and aromatic heterocyclicgroup for R¹ may be substituted with substituents as described above.Examples of the substituent include a halogen atom, an alkyl group, acycloalkyl group, a bicycloalkyl group, an alkenyl group, a cycloalkenylgroup, a bicycloalkenyl group, an alkynyl group, an aryl group, aheterocyclic group (preferably a 5- or 6-membered substituted orunsubstituted heterocyclic group, that is a monovalent group obtained byremoving one hydrogen atom from an aromatic or non-aromatic heterocycliccompound), a cyano group, a hydroxyl group, a nitro group, a carboxylgroup, an alkoxy group, an aryloxy group, a silyloxy group, aheterocyclic oxy group, an acyloxy group, a thioacyloxy group, athioacylthio group, a carbamoyloxy group, an alkoxycarbonyloxy group, anaryloxycarbonyloxy group, an amino group (including an amino group, analkylamino group and an anilino group), an acylamino group, anaminocarbonylamino group, an alkoxycarbonylamino group, anaryloxycarbonylamino group, a sulfamoylamino group, an alkyl- oraryl-sulfonylamino group, a mercapto group, an alkylthio group, anarylthio group, a heterocyclic thio group, a sulfamoyl group, a sulfogroup, an alkyl- or aryl-sulfinyl group, an alkyl- or aryl-sulfonylgroup, an acyl group, an aryloxycarbonyl group, an alkoxycarbonyl group,an aryloxythiocarbonyl group, an alkoxythiocarbonyl group, a thioacyloxygroup, an (alkylthio)carbonyl group, an (arylthio)carbonyl group, an(arylthio)thiocarbonyl group, an (alkylthio)thiocarbonyl group, athioacylthio group, a carbamoyl group, an aryl- or heterocyclic-azogroup, an imido group, a phosphino group, a phosphinyl group, aphosphinyloxy group, a phosphinylamino group, and a silyl group.

Among these, preferred examples include a halogen atom, an alkyl group,a cycloalkyl group, a bicycloalkyl group, a cycloalkenyl group, abicycloalkenyl group, an aryl group, a heterocyclic group (preferably a5- or 6-membered substituted or unsubstituted heterocyclic group, thatis a monovalent group obtained by removing one hydrogen atom from anaromatic or non-aromatic heterocyclic compound), a cyano group, a nitrogroup, an alkoxy group, an aryloxy group, a heterocyclic oxy group, analkylthio group, an arylthio group, a heterocyclic thio group, an alkyl-or aryl-sulfinyl group, an alkyl- or aryl-sulfonyl group, and a silylgroup.

Also, these substituents may also be further substituted. In that case,examples of the substituents include the substituents described above.

Among the substituents that may be carried by these alkyl group,cycloalkyl group, aryl group and aromatic heterocyclic group, anelectron-withdrawing group is preferred, and a group having a Hammettsubstituent constant σ_(m) value of 0 or more is preferred. The Hammettsubstituent constant σ_(m) value is detailed in, for example, “Lange'sHandbook of Chemistry” 12th edition by J. A. Dean, 1979 (McGraw-Hill),“Kagaku no Ryoiki” special issue, No. 122, pp. 96 to 103, 1979(Nankodo). Among the substituents that may be carried by these alkylgroup, cycloalkyl group, aryl group and aromatic heterocyclic group,more preferred examples include substituents selected from a halogenatom (for example, a fluorine atom, a chlorine atom, a bromine atom, oran iodine atom), an alkoxy group (preferably having 1 to 30 carbonatoms; for example, methoxy, ethoxy, isobutoxy, n-octyloxy, or2-ethylhexyloxy), an aryloxy group (preferably having 6 to 30 carbonatoms; for example, phenoxy or naphthoxy), an alkylthio group(preferably having 1 to 30 carbon atoms; for example, methylthio,ethylthio, n-octylthio, 2-ethylhexylthio, or n-decylthio), an arylthiogroup (preferably having 6 to 30 carbon atoms; for example, phenylthioor naphthylthio), an acyl group (preferably having 1 to 30 carbon atoms,including a formyl group, an alkylcarbonyl group, an arylcarbonyl group,and a heterocyclic carbonyl group; for example, formyl, acetyl,propionyl, isobutyryl, pivaloyl, acryloyl, oleoyl, benzoyl, naphthoyl,furoyl, thienoyl, or nicoinoyl), an alkoxycarbonyl group (preferablyhaving 2 to 30 carbon atoms; for example, methoxycarbonyl,ethoxycarbonyl, benzylcarbonyl, n-octyloxycarbonyl, or2-ethylhexylcarbonyl), and an aryloxycarbonyl group (preferably having 7to 30 carbon atoms; for example, phenoxycarbonyl or naphthoxycarbonyl),

an acyloxy group (preferably having 1 to 30 carbon atoms, including aformyloxy group, an alkylcarbonyloxy group, an arylcarbonyloxy group,and a heterocyclic carbonyloxy group; for example, formyloxy, acetyloxy,propionyloxy, isobutyryloxy, pivaloyloxy, acryloyloxy, oleoyloxy,benzoyloxy, naphthoyloxy, furoyloxy, thienoyloxy, or nicoinoyloxy), analkyl- or arylsulfonyl group (preferably an alkylsulfonyl group having 2to 30 carbon atoms, or an arylsulfonyl group having 6 to 30 carbonatoms; for example, methanesulfonyl, ethanesulfonyl, n-octanesulfonyl,benzenesulfonyl, or naphthalenesulfonyl), a cyano group, analkoxycarbonyloxy group (preferably having 2 to 30 carbon atoms; forexample, methoxycarbonyloxy, ethoxycarbonyloxy, or2-ethylhexyloxycarbonyloxy), an aryloxycarbonyloxy group (preferablyhaving 7 to 30 carbon atoms; for example, phenoxycarbonyloxy,4-methylphenoxycarbonyloxy, or naphthyloxycarbonyloxy), analkoxythiocarbonyl group (preferably having 2 to 30 carbon atoms;methoxythiocarbonyl, ethoxythiocarbonyl, 2-ethylhexyloxythiocarbonyl, orn-dodecyloxythiocarbonyl), an aryloxythiocarbonyl group (preferablyhaving 7 to 30 carbon atoms; for example, phenyloxythiocarbonyl,3-methylphenyloxythiocarbonyl, or naphthyloxythiocarbonyl), an(alkylthio)carbonyl group (preferably having 2 to 30 carbon atoms; forexample, (methylthio)carbonyl, (ethylthio)carbonyl, or(isopropylthio)carbonyl, (2-ethylhexylthio)carbonyl), an(arylthio)carbonyl group (preferably having 7 to 30 carbon atoms;(phenylthio)carbonyl or (naphthylthio)carbonyl), a thioacyloxy group(preferably having 1 to 30 carbon atoms, including a thioformyloxygroup, an alkylcarbothioyloxy group, an arylcarbothioyloxy group, and aheterocyclic carbothioyloxy group; for example, thioformyloxy,thioacetyloxy, thiopropionyloxy, thioisobutyryloxy, thiopivaloyloxy,thioacryloyloxy, thiooleoyloxy, thiobenzoyloxy, thionaphthoyloxy,thiofuroyloxy, thiothienoyloxy, or thionicoinoyloxy),an (alkylthio)thiocarbonyl group (preferably having 2 to 30 carbonatoms; for example, (methylthio)thiocarbonyl, (ethylthio)thiocarbonyl,or (2-ethylhexylthio)thiocarbonyl), an (arylthio)thiocarbonyl group(preferably having 7 to 30 carbon atoms, including (phenylthio)carbonyl)or (naphthylthio)thiocarbonyl)), and a thioactylthio group (preferablyhaving 1 to 30 carbon atoms, including a thioformylthio group, analkylcarbothioylthio group, an arylcarbothioylthio group, and aheterocyclic carbothioylthio group; for example, thioformylthio,thioacetylthio, thiopropionylthio, thioisobutyrylthio, thiopivaloylthio,thioacryloylthio, thiooleoylthio, thiobenzoylthio, thionaphthoylthio,thiofuroylthio, thiothienoylthio, or thionicoinoylthio).

When p is 2, in the case where two R¹'s are bonded to each other andform a ring, examples of the cyclic structure include a cycloalkylgroup, an aryl group, or an aromatic heterocyclic group, and in regardto these, the same groups as R¹ described above may be mentioned asexamples.

In the present invention, R¹ is preferably an alkyl group, a cycloalkylgroup, an aryl group or an aromatic heterocyclic group; preferably analkyl group or an aryl group; and most preferably an alkyl group.

The structural unit represented by Formula (I) is preferably astructural unit represented by Formula (I-1), (I-2) or (I-3).

In Formula (I-1), R¹′ and R¹″ each independently represent a hydrogenatom, an alkyl group, a cycloalkyl group, an aryl group or an aromaticheterocyclic group. R¹′ and R¹″ have the same meaning as R¹ in Formula(I), and preferable ranges thereof are also the same.

R¹′ and R¹″ may bond with each other to form a ring. When R¹′ and R¹″are bonded to each other and form a ring, examples of the cyclicstructure include a cycloalkyl group, an aryl group, or an aromaticheterocyclic group, and in regard to these, the same groups as R¹described above may be mentioned as examples.

In Formula (I-2), p′ represents 0, 1 or 2; preferably 0 or 2; and morepreferably 0.

Among the structural units represented by the Formulas (I-1) to (I-3),the structural unit represented by Formula (I-1) or (I-2) is preferred,and the structural unit represented by Formula (I-1) is most preferred.

The organic semiconductor polymer of the present invention is a polymerhaving at least the structural unit represented by Formula (I); however,the polymer may be any one of a homopolymer formed from one kind of thestructural unit represented by Formula (I), a co-polymer of acombination of any of the structural units of Formulae (I-1) to (I-3),and a co-polymer with a structural unit other than the structural unitof Formula (I).

In the case of a co-polymer, regarding the structural unit other thanthe structural unit represented by Formula (I) of the present invention,the structural unit which can be linked each other to the structuralunits represented by Formula (I) by a π-electron conjugated system isused. Any structural unit may be used as long as such structural unitscan be conjugated by a π-electron conjugated system and the π-electronconjugated system can cover the entire polymer molecule.

Examples of the structural unit other than the structural unitrepresented by Formula (I) of the present invention that forms aco-polymer, include a silacyclopentadithiophene structural unit, acyclopentadithiazole structural unit, a benzothiazole structural unit, athiadiazoloquinoxaline structural unit, a cyclopentadithiophenestructural unit, a cyclopentadithiophene oxide structural unit, abenzoisothiazole structural unit, a benzothiazole structural unit, athiophene oxide structural unit, a thienothiophene structural unit, athienothiophene oxide structural unit, a dithienothiophene structuralunit, a dithienothiophene oxide structural unit, a tetrahydroisoindolestructural unit, a fluorene structural unit, a fluorenone structuralunit, an indenofluorene structural unit, a thiazole structural unit, aselenophene structural unit, a silol structural unit, a thiazolothiazolestructural unit, a thienothiophene structural unit, a naphthothiadiazolestructural unit, a thienopyrazine structural unit, an oxazole structuralunit, an imidazole structural unit, a pyrimidine structural unit, abenzoxazole structural unit, a benzimidazole structural unit, athienothiazole structural unit, a dithienopyrrole structural unit, acarbazole structural unit, a benzodithiophene structural unit, and acyclopentadipyridine structural unit.

These structural units can be preferably represented by Formulas (1) to(36) or Formula (II) that will be described below.

In Formulas (1) to (36), R¹¹, R¹² and R¹⁸ each independently represent ahydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, aheterocyclic group, an alkoxy group or an aryloxy group. R¹³ to R¹⁷ eachindependently represent a hydrogen atom or a substituent. Preferredexamples of the substituent include a halogen atom, an alkyl group, acycloalkyl group, an aryl group, a heterocyclic group, an alkoxy group,an aryloxy group, a cyano group, a hydroxyl group, an acyl group, analkoxycarbonyl group, an aryloxycarbonyl group, and an alkyl- oraryl-sulfonyl group. X² and Y¹ each independently represent CH₂, O or S.Y² represents S or Se.

The alkyl group, cycloalkyl group and aryl group for R¹¹, R¹², R¹⁸ andR¹³ to R¹⁷ have the same meanings as R¹ for Formula (I), respectively,and preferred ranges are also the same. The heterocyclic group, alkoxygroup or aryloxy group for R¹¹, R¹², R¹⁸ and R¹³ to R¹⁷, and the halogenatom, acyl group, alkoxycarbonyl group, aryloxycarbonyl group, andalkyl- or arylsulfonyl group for R¹³ to R¹⁷ have the same meanings asthe halogen atom, acyl group, alkoxycarbonyl group, aryloxycarbonylgroup, and alkyl- or arylsulfonyl group listed as the substituents thatmay be carried by the alkyl group, cycloalkyl group, aryl group andaromatic heterocyclic group for R¹, respectively, and preferred rangesare also the same.

Among these, structural units represented by (1), (2), (3), (12), (14),(20), (22), (25), (27), and (35), and a structural unit represented byFormula (II) that will be described below are preferred, and structuralunits represented by (1), (20), and (25), and a structural unitrepresented by Formula (II) that will be described below are morepreferred.

When the polymer having a structural unit represented by Formula (I) ofthe present invention is a co-polymer, a co-polymer of a structural unitrepresented by Formula (I) of the present invention and a structuralunit represented by Formula (II) described below is particularlypreferred.

In Formula (II), Z¹ and Z² each independently represent S, O, Se or Te;and Y represents C(R²¹) or N. R and R²¹ each independently represent ahydrogen atom or a substituent.

Examples of the substituents for R and R²¹ include the substituentswhich may be carried by the alkyl group, cycloalkyl group, aryl groupand aromatic heterocyclic group for R¹.

R is preferably an alkyl group, —SO_(p)X¹, —CN, —NO₂, —P(═O)(OR²²)(OR²³)or —C(R²⁴)═C(CN)₂; and further preferably —SO_(p)X¹, —CN, —NO₂,—P(═O)(OR²²)(OR²³) or —C(R²⁴)═C(CN)₂. X¹ represents a hydrogen atom, analkyl group, a cycloalkyl group, an aryl group, an aromatic heterocyclicgroup or —NR²⁵(R²⁶). R²² to R²⁶ each independently represent a hydrogenatom, an alkyl group, a cycloalkyl group, an aryl group or an aromaticheterocyclic group. R²⁵ and R²⁶ may bond with each other to form a ring.p represents 1 or 2.

The alkyl group, cycloalkyl group, aryl group and aromatic heterocyclicgroup for R²² to R²⁶ have the same meanings as the alkyl group,cycloalkyl group, aryl group and aromatic heterocyclic group for R¹,respectively, and preferred ranges are also the same.

Z¹ and Z² each are preferably S, O or Se; more preferably S or O; andmost preferably S. Y is preferably CH or N; and more preferably N.

R is preferably —SO_(p)X¹. X¹ is preferably a hydrogen atom, an alkylgroup, a cycloalkyl group, an aryl group or an aromatic heterocyclicgroup; more preferably an alkyl group, a cycloalkyl group or an arylgroup; and further preferably an alkyl group or an aryl group.

p is preferably 2.

R²¹ to R²⁶ and X¹ more preferably do not contain the double bond of avinyl group or an allyl group, an acetylene group, or the cyclic etherof an epoxy group or an oxetane group, from the viewpoint of obtainingexcellent thermally stability of the polymer film thus obtained.

Specific examples of polymer having a structural unit represented byFormula (I) are shown in the followings, but the present invention isnot limited thereto.

The structural unit represented by Formula (I) of the present inventioncan be easily synthesized by a cross-coupling reaction or the likereferring to, for example, the methods described in J. Chem. Soc. Chem.Commun, p. 866 (1979) and Angew. Chem. Int. Ed. 25, p. 508 (1986)(Suzuki reaction, Yamamoto reaction, Heck reaction, Stille reaction,Sonogashira-Hagihara reaction, Kumada-Corriu reaction, Riecke reaction,and McCullogh reaction) or methods equivalent to these methods. Here,the organotin compound of the raw material can be easily synthesized by,for example, the method described in Chem. Lett. 1977, p. 301 or thelike, and regarding the raw material of the co-polymer andcopolymerization, synthesis can be similarly easily carried outreferring to the methods described in Synthetic Communications, Vol. 11,No. 7, p. 513 (1981); Makromoleculare Chemistry, Rapid Communications,vol. 12, p. 489 (1992); and Polymer, Vol. 38, p. 1221 (1997), or methodsequivalent thereto.

<Organic Semiconductor Polymer>

A polymer having the structural unit represented by Formula (I) of thepresent invention is useful as an organic semiconductor polymer. Anorganic semiconductor polymer is a polymer of an organic compoundcapable of exhibiting the properties as a semiconductor, and the polymerof the present invention is particularly useful as a p-type organicsemiconductor polymer. Meanwhile, a p-type organic semiconductorcompound, including a polymer, is generally a π-electron conjugatedcompound having a highest occupied molecular orbital (HOMO) energy levelof 4.5 eV to 6.0 eV.

Organic semiconductor polymers are used in organic electroluminescentelements that emit light when electricity is passed, organicphotoelectric conversion elements that generate power when irradiatedwith light, organic thin film transistor elements that control theamount of current or the amount of voltage, electrochemical sensors,printable circuits, and the like, which are used in the field of organicelectronics. In the present invention, it is preferable to use organicsemiconductor polymer in photovoltaic cells, and particularly in organicthin film solar cells.

<Composition for Organic Semiconductor Material>

The composition for organic semiconductor material of the presentinvention will be described.

The polymer having a structural unit represented by Formula (I) of thepresent invention is useful as a p-type organic semiconductor polymer,and the composition for organic semiconductor material of the presentinvention contains this polymer having a structural unit represented byFormula (I) and an n-type semiconductor compound, and particularlyaccording to the present invention, it is preferable that thecomposition for organic semiconductor material contains an n-typeorganic semiconductor compound. Furthermore, if necessary, thecomposition for organic semiconductor material may contain a p-typeorganic semiconductor compound other than the polymer having astructural unit represented by Formula (I), and a compound other thansemiconductor (for example, examples of the other p-type semiconductorcompound include poly-3-hexylthiophene (P3HT),poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV),poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene](MDMO-PPV),poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazole-4,8-diyl)](F8BT); and examples of the compound other than semiconductor includeother polymers such as a polyester-based resin and a methacrylic resinthat will be described below). When the mass of the composition isdesignated as 100, the composition contains 10 to 90 of the polymerhaving a structural unit represented by Formula (I), 10 to 90 of ann-type organic semiconductor compound, 0 to 50 of a p-type organicsemiconductor compound other than the polymer having a structural unitrepresented by Formula (I), and 0 to 50 of a compound other thansemiconductor.

(N-Type Organic Semiconductor Compound)

There are no particular limitations on the n-type organic semiconductorcompound. Generally, the n-type organic semiconductor compound is aπ-electron conjugated compound having a minimum unoccupied molecularorbital (LUMO) energy level of 3.5 eV to 4.5 eV, and examples thereofinclude fullerene or a derivative thereof; octaazaporphyrin; perfluorocompounds obtained by substituting the hydrogen atoms of a p-typeorganic semiconductor compound with fluorine atoms (for example,perfluoropentacene or perfluorophthalocyanine); and polymer compoundscontaining aromatic carboxylic acid anhydrides or imidation productsthereof as skeletal structures, such as naphthalenetetracarboxylic acidanhydride, naphthalenetetracarboxylic acid diimide,perylenetetracarboxylic acid anhydride, and perylenetetracarboxylic aciddiimide.

Among these n-type organic semiconductor compounds, fullerene or aderivative thereof is preferred, and fullerene or a derivative thereofis more preferred, so that electrical charge separation from the organicsemiconductor polymer having a structural unit represented by Formula(I) of the present invention (p-type organic semiconductor compound) canbe achieved rapidly and efficiently.

Examples of the fullerenes, carbon nanotubes, carbon nanohorns or aderivative thereof include fullerene C₆₀, fullerene C₇₀, fullerene C₇₆,fullerene C₇₈, fullerene C₈₄, fullerene C₂₄₀, fullerene C₅₄₀, mixedfullerene, fullerene nanotube, and a fullerene derivative a part ofwhich is substituted with a hydrogen atom, a halogen atom, a substitutedor unsubstituted alkyl group, alkenyl group, alkynyl group, aryl group,heteroaryl group, cycloalkyl group, silyl group, ether group, thioethergroup, amino group or silyl group.

As the fullerene derivative, a phenyl-C₆₁-butyric acid ester, adiphenyl-C₆₂-bis(butyric acid ester), a phenyl-C₇₁-butyric acid ester, aphenyl-C₈₅-butyric acid ester, or a thienyl-C₆₁-butyric acid ester ispreferred, and the number of carbon atoms of the alcohol moiety of thebutyric acid esters is preferably 1 to 30, more preferably 1 to 8, evenmore preferably 1 to 4, and most preferably 1.

Preferred examples of the fullerene derivative includephenyl-C₆₁-butyric acid methyl ester ([60]PCBM), phenyl-C₆₁-butyric acidn-butyl ester ([60]PCBnB), phenyl-C₆₁-butyric acid isobutyl ester([60]PCBiB), phenyl-C₆₁-butyric acid n-hexyl ester ([60]PCBH),phenyl-C₆₁-butyric acid n-octyl ester ([60]PCBO),diphenyl-C₆₂-bis(butyric acid methyl ester)(bis[60]PCBM),phenyl-C₇₁-butyric acid methyl ester ([70]PCBM), phenyl-C₈₅-butyric acidmethyl ester ([84]PCBM), thienyl-C₆₁-butyric acid methyl ester([60]ThCBM), C₆₀ pyrrolidine tris-acid, C₆₀ pyrrolidine tris-acid ethylester, N-methylfulleropyrrolidine (MP-C₆₀), (1,2-methanofullereneC₆₀)-61-carboxylic acid, (1,2-methanofullerene C₆₀)-61-carboxylic acidt-butyl ester, metallocene-doped fullerene of JP-A-2008-130889 and thelike, and fullerene having a cyclic ether group of U.S. Pat. No.7,329,709 and the like.

The composition for organic semiconductor material of the presentinvention may contain another p-type semiconductor compound (forexamples, a condensed low-molecular weight polycyclic aromatic compound,oligomer or polymer), together with the polymer having a structural unitrepresented by Formula (I) of the present invention.

Examples of the condensed low-molecular weight polycyclic aromaticcompound as the p-type semiconductor compound include compounds such asanthracene, tetracene, pentacene, hexacene, heptacene, chrysene, pysene,fuluminene, pyrene, perpyrene, perylene, terylene, quoterylene,coronene, ovalene, circumanthracene, bisanthene, zethrene,heptazethrene, pyranthrene, violanthene, isoviolanthene, circobiphenyl,and anthradithiophene; porphyrin or copper phthaloeyanine,tetrathiafulvalene (TTF)-tetracyanoquinodimethane (TCNQ) complex,bisethylenetetrathiafulvalene (BEDTTTF)-perchloric acid complex, andderivatives or precursors thereof.

Examples of a derivative containing the condensed polycyclic compoundinclude pentacene compounds having a substituent disclosed in WO03/16599, WO 03/28125, U.S. Pat. No. 6,690,029 and JP-A-2004-107216;pentacene precursors disclosed in US 2003/136964; substituted aceneswith a trialkylsilylethynyl group disclosed in J. Amer. Chem. Soc., vol.127, p. 4986 (2005), J. Amer. Chem. Soc., vol. 123, p. 9482 (2001), andJ. Amer. Chem. Soc., vol. 130, p. 2706 (2008); and porphyrin-seriescompounds disclosed in JP-A-2008-16834.

Examples of the conjugate polymer or oligomer as the p-typesemiconductor compound include polymer materials such as polythiophenesuch as poly(3-hexylthiophene) (P3HT) and oligomer thereof;polythiophene having a polymerizable group described in Technical Digestof the International PVSEC-17, Fukuoka, Japan, 2007. p. 1225;polythiophene-thienothiophene co-polymer described in Nature Material,(2006) vol. 5, p. 328; polythiophene-diketopyrrolopyrrol co-polymerdescribed in WO 2008/000664; polythiophene-thiazolothiazole co-polymerdescribed in Adv. Mater, 2007, p. 4160; polythiophene co-polymer such asPCPDTBT described in Nature Mat. vol. 6 (2007), p. 497; polypyrrole andits oligomer; polyaniline, polyphenylene and its oligomer, polyphenylenevinylene and its oligomer; polythienylene vinylene and its oligomer; andδ conjugate type polymer such as polyacethylene, polydiacetylene,polysilane, and polygermane. As an oligomer material, appropriately usedare oligomers such as α-sexithiophene, α,ω-dihexyl-α-sexithiophene,α,ω-dihexyl-α-quinquethiphene, α,ω-bis(3-butoxypropyl)-α-sexithiophene,all of which are thiophene hexamer.

(Photoelectric Conversion Layer)

The composition for organic semiconductor material of the presentinvention is preferably used as a composition for coating of aphotoelectric conversion layer (particularly a bulk heterojunctionlayer). The mixing ratio of the p-type organic semiconductor compoundwhich is an electron donor material, to the n-type semiconductorcompound which is an electron accepting material is adjusted such thatthe photoelectric conversion efficiency would become the highest.Usually, the mixing ratio is selected from the range of 10:90 to 90:10,and preferably 20:80 to 80:20, as a mass ratio. Regarding the method forforming such a mixed layer, for example, a co-deposition method is used.Alternatively, the mixed layer can also formed by a coating method usinga solvent which can dissolve both the organic materials. In order toincrease the area of the interface at which charge separation of holesand electrons occurs, and to obtain high photoelectric conversionefficiency, a coating method is preferred.

Here, for the purpose of promoting the phase separation of the electrondonating region (donor) and the electron accepting region (acceptor) inthe photoelectric conversion layer, crystallization of the organicmaterials contained in the photoelectric conversion layer,transparentization of the electron transport layer, and the like, thephotoelectric conversion layer may be subjected to a heating treatment(annealing) by various methods. In the case of a dry film forming methodsuch as deposition, for example, there is available a method of heatingthe substrate temperature to 50° C. to 150° C. during film formation. Inthe case of a wet film forming method such as printing or coating, thereis available a method of adjusting the drying temperature after coatingto 50° C. to 150° C. Furthermore, the photoelectric conversion layer mayalso be heated to 50° C. to 150° C. in a post-process, for example,after completion of the formation of a metal negative electrode. As thephase separation is promoted, the carrier mobility increases, and highphotoelectric conversion efficiency can be obtained.

<Photoelectric Conversion Element, Photovoltaic Cell>

Hereinafter, a photoelectric conversion element that uses the polymer ofa structural unit represented by Formula (I) of the present invention orthe composition for organic semiconductor material of the presentinvention, and a photovoltaic cell as a representative example of thephotoelectric conversion element will be described.

In a photovoltaic cell, and particularly in an organic thin film solarcell, the composition for organic semiconductor material of the presentinvention is used as the photoelectric conversion layer described above,and particularly preferably as a bulk heterojunction layer.

Photovoltaic cells, and particularly the organic thin film solar cells,are generally classified into p-i-n junction type organic thin filmsolar cells having a p-i-n trilayer structure, and bulk heterojunctiontype organic thin film solar cells. In the present invention, any ofthem may be used, but since high photoelectric conversion efficiency isobtained easily, the present invention is particularly preferablyapplied to bulk heterojunction type organic thin film solar cells.

In a photovoltaic cell, the photoelectric conversion layer, andparticularly the bulk heterojunction layer in a bulk heterojunction typeorganic thin film solar cell, is formed using the composition fororganic semiconductor material of the present invention. Thisphotoelectric conversion layer may be composed of a single layer, or maybe composed of plural layers in which the kinds and mixing ratio of thep-type semiconductor compound, which is an electron donor compound, toan n-type semiconductor compound, which is an electron acceptorcompound, are varied.

This photoelectric conversion layer is provided between a firstelectrode and a second electrode. In the present invention, it ispreferable to provide a hole transport layer between the first electrodeand the photoelectric conversion layer, and it is also preferable toprovide an electron transport layer between the second electrode and thephotoelectric conversion layer. It is particularly preferable to providea hole transport layer between the first electrode and the photoelectricconversion layer, and to provide an electron transport layer between thephotoelectric conversion layer and the second electrode.

As these hole transport layer and electron transport layer are provided,electrical charges generated at the photoelectric conversion layer canbe extracted more efficiently.

(Electrode)

The photoelectric conversion element according to the present inventionincludes at least a first electrode and a second electrode. The firstelectrode and the second electrode are such that any one of them servesas a positive electrode, and the other serves as a negative electrode.Furthermore, in the case of adopting a tandem configuration, a tandemconfiguration can be achieved by using an intermediate electrode.Meanwhile, in the present invention, the electrode through whichprimarily holes flow is referred to as a positive electrode, while theelectrode through which primarily electrons flow is referred to as anegative electrode. Furthermore, in view of the function of having lighttransmissibility or not, an electrode having light transmissibility isreferred to as a transparent electrode, and an electrode having no lighttransmissibility is referred to as a counter electrode or a metalelectrode. Usually, the positive electrode is a transparent electrodehaving light transmissibility, while the negative electrode is a counterelectrode or a metal electrode having no light transmissibility.However, both the first electrode and the second electrode can be madeinto transparent electrodes.

(First Electrode)

The first electrode is a cathode. In the case using it for a solar cell,it is preferably an electrode transmitting a light of from visible lightto near infrared light (380 to 800 nm). Examples of a material which canbe used include transparent conductive metal oxides of indium tin oxide(ITO), SnO₂, and ZnO; a metal nanowire; and a carbon nanotubes. Further,it can be used a conductive polymer selected from the group consistingof derivatives of polypyrrole, polyaniline, polythiophene,polythienylene vinylene, polyazulene, polyisothianaphthene,polycarbazole, polyacethylene, polyphenylene, polyphenylene vinylene,polyacene, polyphenylacetylene, polydiacetylene, and polynaphthalene.Furthermore, a plural number of these electrically conductive compoundscan be combined, and the combination can be used in the positiveelectrode. Meanwhile, in the case where light transmissibility is notrequired, the positive electrode may be formed using a metal materialsuch as nickel, molybdenum, silver, tungsten, or gold. In the case wherea transparent solar cell is to be produced, the transmittance of thepositive electrode is preferably such that the average lighttransmittance at the thickness used in solar cells (for example, athickness of 0.2 μm) in the wavelength range of 380 nm to 800 nm ispreferably 75% or more, and more preferably 85% or more.

(Second Electrode)

The second electrode of the present invention is a negative electrode,and is a metal negative electrode having a standard electrode potentialof a positive value.

The negative electrode may be an independent layer made of a conductivematerial, in addition to the material which has conductivity, it may beused a resin which holds such material together. As a conductingmaterial used for a negative electrode, it can be used: a metal, analloy, an electric conductive compound, and a mixture thereof, which hasa small work function (4 eV or less). Specific examples of suchelectrode material include sodium, a sodium potassium alloy, magnesium,lithium, a magnesium/copper mixture, a magnesium/silver mixture, amagnesium/aluminum mixture, a magnesium/indium mixture, analuminum/aluminium oxide (Al₂O₃) mixture, indium, a lithium/aluminiummixture and a rare earth metal. Among these, from the viewpoint of anelectron taking out property and resistivity to oxidation, a mixture ofthese metals and the second metal having a larger work function thanthese metals is suitable. Examples of these include a magnesium/silvermixture, a magnesium/aluminum mixture, a magnesium/indium mixture, analuminum/aluminium oxide (Al₂O₃) mixture, a lithium/aluminum mixture andaluminium. A negative electrode can be produced by using these electrodematerials with a method such as a vacuum evaporation method or asputtering method. Moreover, the coating thickness is usually chosenfrom the range of 10 nm to 5 μm, preferably from the range of 50 to 200nm.

When a metallic material is used as a conducting material of thenegative electrode, the light arriving at the negative electrode will bereflected and will be also reflected by the first electrode side, andthis light can be reused. As a result, the light is again absorbed bythe photoelectric conversion layer to result in improvement ofphotoelectric conversion efficiency. This is desirable. Moreover, thenegative electrode may be nanoparticles, nanowires, or a nanostructurematerial which is made of a metal (for example, gold, silver, copper,platinum, rhodium, ruthenium, aluminium, magnesium and indium) andcarbon. When it is a dispersion of nanowires, a transparent and highconductive negative electrode can be formed by a coating method, and itis preferable.

When the negative electrode side is made to be light transparent, it canbe achieved as follows. After producing thin film of a conductivematerial suitable for negative electrodes, such as an aluminium, analuminum alloy, silver or a silver compound to have a coating thicknessof about 1 to 20 nm, a light transmitting negative electrode can beprepared by providing on the thin film with the membrane of a conductivelight transparent material cited in the description of theabove-mentioned positive electrode.

(Hole Transport Layer)

In the present invention, it is preferable to provide a hole transportlayer between the first electrode and the photoelectric conversionlayer.

Examples of the electrically conductive polymer that forms the holetransport layer include polythiophene, polypyrrole, polyaniline,polyphenylenevinylene, polyphenylene, polyacetylene, polyquinoxaline,polyoxadiazole, polybenzothiadiazole, and polymers having a pluralnumber of these conductive skeletal structures.

Among these, polythiophene and derivatives thereof are preferred, andpolyethylenedioxythiophene and polythienothiophene are particularlypreferred. These polythiophenes are usually partially oxidized in orderto obtain electrical conductivity. The electrical conductivity of theconductive polymer can be regulated by the degree of partial oxidation(doping amount), and as the doping amount increases, electricalconductivity increases. Since polythiophene becomes cationic as a resultof partial oxidation, a counter anion for neutralizing the electricalcharge is required. Examples of such a polythiophene includepolyethylenedioxythiophene having polystyrene sulfonate as a counter ion(PEDOT-PSS), and polyethylenedioxythiophene having p-toluenesulfonicacid as a counter anion (PEDOT-TsO).

In the hole transport layer, another polymer may also be added theretoas long as desired electrical conductivity is not impaired. The otherpolymer is added for the purpose of enhancing coatability, or for thepurpose of increasing the film strength. Examples of the other polymerinclude thermoplastic resins such as a polyester resin, a methacrylicresin, a methacrylic acid-maleic acid co-polymer, a polystyrene resin, atransparent fluororesin, a polyimide, a fluorinated polyimide resin, apolyamide resin, a polyamideimide resin, a polyether imide resin, acellulose acylate resin, a polyurethane resin, a polyether ether ketoneresin, a polycarbonate resin, an alicyclic polyolefin resin, apolyallylate resin, a polyether sulfone resin, a polysulfone resin, acycloolefin co-polymer, a fluorene ring-modified polycarbonate resin, analicyclic-modified polycarbonate resin, a fluorene ring-modifiedpolyester resin, and an acryloyl compound; and hydrophilic polymers suchas gelatin, polyvinyl alcohol, polyacrylic acid, polyacrylamide,polyvinylpyrrolidone, polyvinylpyridine, and polyvinylimidazole. Thesepolymers may be crosslinked so as to increase the film strength.

Furthermore, in the hole transport layer, the cyan compounds and thelike described in WO 2006/019270 can be used. In addition, to the holetransport layer which has a LUMO energy level shallower than the LUMOenergy level of the n-type semiconductor compound used for aphotoelectric conversion layer, there is provided an electron blockingfunction having a rectification effect by which the electron generatedin the photoelectric conversion layer is not passed to the anode side.The above-described hole transport layer is also called an electronblocking layer, and it is more preferable to use a hole transport layerhaving such function. Examples of these materials include a triarylamine compound described in JP-A-5-271166, a metal oxide such asmolybdenum oxide, nickel oxide tungsten oxide and vanadium oxide.Moreover, the layer which consists of the p-type semiconductor compoundused for the photoelectric conversion layer can also be used. As a meansto form these layers, although any one of a vacuum deposition method anda solution coating method can be used, preferably used is a solutioncoating method. When a coated layer is formed as an under layer beforeforming a photoelectric conversion layer, it will have an effect ofleveling the coating surface. This will result in decreasing a leakingeffect and it is preferable.

The thickness of the hole transport layer is preferably 10 nm to 500 nm,and more preferably 20 nm to 200 nm.

(Electron Transport Layer)

In the present invention, it is preferable to provide an electrontransport layer between the second electrode and the photoelectricconversion layer, and it is particularly preferable to provide a holetransport layer between the first electrode and the photoelectricconversion layer and to provide an electron transport layer between thephotoelectric conversion layer and the second electrode.

Examples of the electron transporting material that can be used in theelectron transport layer include the n-type semiconductor compoundsdescribed above in the photoelectric conversion layer, which areelectron-acceptor materials, and the materials described aselectron-transporting and hole-blocking materials in Chemical Review,Vol. 107, pp. 953-1010 (2007). In the present invention, it ispreferable to use an inorganic salt or an inorganic oxide. Preferredexamples of the inorganic salt include alkali metal compounds such aslithium fluoride, sodium fluoride, and cesium fluoride. Various metaloxides are preferably used as materials for electron transport layerhaving high stability, examples thereof include lithium oxide, magnesiumoxide, aluminum oxide, calcium oxide, titanium oxide, zinc oxide,strontium oxide, niobium oxide, ruthenium oxide, indium oxide, zincoxide, and barium oxide. Among these, relatively stable aluminum oxide,titanium oxide, and zinc oxide are more preferred. The film thickness ofthe electron transport layer is 0.1 nm to 500 nm, and preferably 0.5 nmto 300 nm. The electron transport layer can be suitably formed by any ofa wet film forming method based on coating or the like, a dry filmforming method according to a PVD method such as deposition orsputtering, a transfer method, a printing method, and the like.

Meanwhile, the electron transport layer that has a HOMO energy levelthat is deeper than the HOMO energy level of the p-type semiconductorcompound used in the photoelectric conversion layer, is imparted with ahole blocking function of having a rectification effect in which holesproduced in the photoelectric conversion layer are not passed to thenegative electrode side. More preferably, the material having the HOMOenergy level deeper than the HOMO energy level of the n-typesemiconductor compound is used as the electron transport layer. Further,in view of the characteristics of transporting electrons, it ispreferable to use a compound having high electron mobility. Such anelectron transport layer is also called a hole blocking layer, and it ispreferable to use an electron transport layer having such a function. Assuch a material, phenanthrene-based compounds such as bathocuproine;n-type semiconductor compounds such as naphthalenetetracarboxylic acidanhydride, naphthalenetetracarboxylic acid diimide,perylenetetracarboxylic acid anhydride, and perylenetetracarboxylic aciddiimide; n-type inorganic oxides such as titanium oxide, zinc oxide, andgallium oxide; and alkali metal compounds such as lithium fluoride,sodium fluoride, and cesium fluoride, can be used. Furthermore, a layerformed from a simple substance of the n-type semiconductor compound usedin the photoelectric conversion layer can also be used.

(Support)

The support that constitutes the photovoltaic cell of the presentinvention is not particularly limited as long as at least a firstelectrode (positive electrode), a photoelectric conversion layer, and asecond electrode (metal negative electrode), and in a more preferredembodiment, a first electrode (positive electrode), a hole transportlayer, a photoelectric conversion layer, an electron transport layer,and a second electrode (metal negative electrode), can be formed on thesupport and retained thereon. For example, the support can beappropriately selected from a glass plate, a plastic film and the likeaccording to the purpose.

Hereinafter, a plastic film substrate as a representative example of thesupport will be described.

The material, thickness and the like of the plastic film substrate arenot particularly limited and can be appropriately selected according tothe purpose. In the case of producing an organic thin film solar cellhaving light transmissibility, a plastic film substrate having excellenttransmissibility to light, for example, light having a wavelength in therange of 400 nm to 800 nm, is preferred.

Light transmittance can be calculated by measuring the total lighttransmittance and the amount of scattered light using the methoddescribed in JIS K7105, that is, using an integrating sphere type lighttransmittance measuring apparatus, and subtracting the diffusetransmittance from the total light transmittance.

As the material of the plastic film that can be used for the support,specific examples include thermoplastic resins, such as polyesterresins, methacryl resins, methacrylic acid-maleic anhydride co-polymers,polystyrene resins, transparent fluororesins, polyimides,fluoropolyimide resins, polyamide resins, polyamidimide resins,polyetherimide resins, cellulose acylate resins, polyurethane resins,polyether ether ketone resins, polycarbonate resins, alicyclicpolyolefin resins, polyarylate resins, polyether sulfone resins,polysulfone resins, cycloolefin co-polymers, fluorene ring-modifiedpolycarbonate resins, alicyclic-modified polycarbonate resins, fluorenering-modified polyester resins, and acryloyl compounds.

It is preferable that the plastic film substrate be formed from amaterial having heat resistance. Specifically, it is preferable that theplastic film substrate be formed from a material which has heatresistance that satisfies at least any one property of a glasstransition temperature (Tg) of 100° C. or more and a linear thermalexpansion coefficient of 40 ppm·K⁻¹ or less, and also has hightransparency to the wavelength of the exposure light as described above.

Meanwhile, the Tg and linear expansion coefficient of a plastic film aremeasured by the method for measuring the transition temperature of aplastic as described in JIS K7121, and the method for testing the linearexpansion coefficient by a thermomechanical analysis for a plastic asdescribed in JIS K7197, and in the present invention, the valuesmeasured by this method are used.

Tg and the linear expansion coefficient of the plastic film substratemay be controlled by an additive or the like. Examples of such athermoplastic resin excellent in heat resistance includes polyethylenenaphthalate (PEN: 120° C.), polycarbonate (PC: 140° C.),alicyclicpolyolefin (e.g., Nippon Zeon's Zeonoa 1600: 160° C.),polyarylate (PAr: 210° C.), polyether sulfone (PES: 220° C.),polysulfone (PSF: 190° C.), cycloolefin co-polymer (COC, compounddescribed in JP-A 2001-150584: 162° C.), fluorene ring-modifiedpolycarbonate (BCF-PC, compound described in JP-A 2000-227603: 225° C.),alicyclic-modified polycarbonate (IP-PC, compound described in JP-A2000-227603: 205° C.), acryloyl compounds (compounds described in JP-A2002-80616: 300° C. or more), and polyimide (the parenthesized data areTg). These are suitable as the base material according to the presentinvention. In particular, for high transparency, use of alicyclicpolyolefin is preferred.

The plastic film that is used as the support is required to betransparent to light. More specifically, the light transmittance tolight having a wavelength in the range of 400 nm to 800 nm is usuallypreferably 80% or more, more preferably 85% or more, and even morepreferably 90% or more.

There are no particular limitations on the thickness of the plasticfilm, the thickness is typically 1 μm to 800 μm, and preferably 10 μm to300 μm.

On the back surface side (surface on the side where a positive electrodeis not formed) of the plastic film, a functional layer which is publiclyknown may be provided. Examples thereof include a gas barrier layer, amatting agent layer, a reflection preventive layer, a hard coat layer,an anti-fog layer, and an anti-fouling layer. In addition to these,functional layers are described in detail in paragraphs [0036] to [0038]of JP-A-2006-289627.

(Easily Adhesive Layer/Undercoat Layer)

The front surface (surface on the side where a positive electrode isformed) of the plastic film may have an easily adhesive layer or anundercoat layer from the viewpoint of enhancing adhesiveness. The easilyadhesive layer or undercoat layer may be a single layer, or may be amultilayer.

For the formation of the easily adhesive layer or undercoat layer,various hydrophilic primer coating polymers are used. Examples of thehydrophilic primer coating polymers that are used in the presentinvention include water-soluble polymers such as gelatin, gelatinderivatives, casein, agar, sodium alginate, starch, and polyvinylalcohol; cellulose esters such as carboxymethyl cellulose andhydroxyethyl cellulose; latex polymers such as vinyl chloride-containingco-polymers, vinylidene chloride-containing co-polymers, acrylic acidester-containing co-polymers, vinyl acetate-containing co-polymers, andbutadiene-containing co-polymers; polyacrylic acid co-polymers, andmaleic anhydride co-polymers.

The coating film thickness after drying of the easily adhesive layer orundercoat layer is preferably in the range of 50 nm to 2 μm. Also, inthe case of using the support as a provisional support, the supportsurface can be subjected to a treatment for easy detachability.

(Functional Layer)

On the back surface side (surface on the side where a positive electrodeis not formed) of the support, a functional layer may be provided.Examples thereof include a gas barrier layer, a matting agent layer, areflection preventive layer, a hard coat layer, an anti-fog layer, ananti-fouling layer, and an easily adhesive layer. In addition to these,functional layers are described in detail in paragraphs [0036] to [0038]of JP-A-2006-289627, and the functional layers described therein may beprovided in accordance with the purpose.

<Recombination Layer>

The solar cell according to the present invention may have a so-calledtandem type configuration in which plural photoelectric conversionlayers are laminated. The tandem type configuration may be of seriesconnection type or parallel connection type.

In a tandem type element having two photoelectric conversion layers, arecombination layer is provided between the two photoelectric conversionlayers. As the material for the recombination layer, an ultrathin filmof an electrically conductive material is used. Preferred examples ofthe conductive material include gold, silver, aluminum, platinum,titanium oxide, and ruthenium oxide. Among these, silver that isrelatively inexpensive and stable is preferred. The film thickness ofthe recombination layer is 0.01 nm to 5 nm, preferably 0.1 nm to 1 nm,and particularly preferably 0.2 nm to 0.6 nm. There are no particularlimitations on the method for forming the recombination layer, and therecombination layer can be formed by, for example, a PVD method such asa vacuum deposition method, a sputtering method, or an ion platingmethod.

<Other Semiconductor Layers>

If necessary, the photovoltaic cell may also include auxiliary layerssuch as a hole inhibiting layer and an exciton diffusion preventionlayer. Meanwhile, in the present invention, the photovoltaic cell mayinclude layers such as a photoelectric conversion layer, a holetransport layer, a hole injection layer, an electron transport layer, anelectron injection layer, an electron inhibiting layer, a holeinhibiting layer, and an exciton diffusion prevention layer, which areformed between the first electrode and the second electrode (thepositive electrode and the metal negative electrode). The layers whichtransport electrons or holes will be collectively referred to as“semiconductor layers”.

<Protective Layer>

The photovoltaic cell according to the present invention may be coatedwith a protective layer. Examples of the material that is contained inthe protective layer include inorganic materials, including metal oxidessuch as magnesium oxide, aluminum oxide, silicon oxide (SiOx), titaniumoxide, germanium oxide, yttrium oxide, zirconium oxide, and hafniumoxide; metal nitrides such as silicon nitride (SiNx); metal nitrideoxides (metal oxynitrides) such as silicon nitride oxide (SiOxNy); metalfluorides such as lithium fluoride, magnesium fluoride, aluminumfluoride, and calcium fluoride; and diamond-like carbon (DLC). Examplesof organic materials include polymers such as polyethylene,polypropylene, polyvinylidene fluoride, polyparaxylylene, and polyvinylalcohol. Among these, oxides, nitrides and nitride oxides of metals, andDLC are preferred, and oxides, nitrides and nitride oxides of siliconand aluminum are particularly preferred. The protective layer may have aconfiguration of a single layer or a multilayer.

There are no particular limitations on the method for forming theprotective layer, and for example, PVD methods such as a vacuumdeposition method, a sputtering method, an MBE (molecular beam epitaxy)method, a cluster ion beam method, an ion plating method, and a plasmapolymerization method; various CVD methods including an atomic layerdeposition method (ALD method or ALE method), coating methods, printingmethods, and transfer methods can be applied. In the present invention,the protective layer may be used as a conductive layer.

<Gas Barrier Layer>

A protective layer that is intended to inhibit the penetration of activefactors such as water molecules or oxygen molecules is also particularlyreferred to as a gas barrier layer, and the photovoltaic cell,particularly organic thin film solar cell, according to the presentinvention preferably has a gas barrier layer. The gas barrier layer isnot particularly limited as long as it is a layer which blocks activefactors such as water molecules or oxygen molecules, and those materialspreviously exemplified for the protective layer are usually used. Thesemay be pure materials, or may be mixtures having plural compositions, orgraded compositions. Among these, oxides, nitrides, and nitride oxidesof silicon and aluminum are preferred.

The gas barrier layer may be a single layer, or may include plurallayers. For the gas barrier layer, a laminate of an organic materiallayer and an inorganic material layer may be used, or an alternatinglaminate of plural inorganic material layers and plural organic materiallayers may also be used. The organic material layer is not particularlylimited as long as the layer is smooth, but preferred examples includelayers formed from polymerization products of (meth)acrylates. Regardingthe inorganic material layer, the materials for the protective layerdescribed above are preferred, and oxides, nitrides, and nitride oxidesof silicon and aluminum are particularly preferred.

Not specifically defined, the thickness of the inorganic material layeris generally within a range of from 5 to 500 nm per one layer,preferably from 10 to 200 nm per one layer. The inorganic material layermay be a laminate composed of a plurality of sub-layers. In this case,each sub-layer may have the same composition, or a differentcomposition. In addition, as so mentioned hereinabove and as disclosedin US 2004/00046497, the inorganic layers may be gradation layers ofwhich the composition changes continuously in the thickness direction ofthe layer, with no definite boundary to the adjacent inorganic layer.

The thickness of the photovoltaic cell according to the presentinvention is not particularly limited. In the case of producing anorganic thin film solar cell having light transmissibility, thethickness is preferably 50 μm to 1 mm, and more preferably 100 μm to 500μm.

When a module for sunlight power generation is produced using thephotovoltaic cell according to the present invention, reference can bemade to the descriptions in Yoshihiro Hamakawa, “Taiyoko Hatsuden:Saishin no Gijutsu to Shisutemu (Photovoltaic power generation: LatestTechnologies and Systems)”, CMC Publishing (2000), and the like.

The polymer having a structural unit represented by Formula (I) of thepresent invention, and the photovoltaic cell have been described, and insome embodiments, the polymer having a structural unit represented byFormula (I) of the present invention can be used in other elements andsystems. For example, such a polymer can be used in suitable organicsemiconductor elements such as field effect transistors, photodetectors(for example, infrared light detectors), photovoltaic detectors, imagepickup elements (for example, RGB image pickup elements of cameras ormedical image pickup systems), light emitting diodes (LED) (for example,organic LED's or infrared or near-infrared LED's), laser elements,conversion layers (for example, layers that convert visible lightemission to infrared light emission), amplifier radiators for electriccommunication (for example, doping agent for fibers), memory elements(for example, holographic memory elements), and electrochromic elements(for example, electrochromic displays).

EXAMPLES

The present invention will be described in more detail based on thefollowing examples. The materials, used amounts, proportions,treatments, treatment procedures and the like indicated in the followingExamples can be appropriately modified as long as the purport of thepresent invention is maintained. It is therefore understood that thepresent invention is by no means intended to be limited to the specificexamples below.

Example 1 Synthesis of Polymer 1

Compound 1-C was synthesized according to the following scheme, andpolymer 1 was synthesized from this compound 1-C.

In a nitrogen atmosphere, 3.2 g of compound (1-A) (synthesized by thesynthesis method for Compound 5 described in Organic Letters, Vol. 12,p. 5478-5481 (2010)) was dissolved in 50 mL of dry tetrahydrofuran(THF), and the solution was cooled to an internal temperature of −80° C.or lower. 6.9 mL of n-butyllithium (1.6 mol/L hexane solution) was addeddropwise thereto at an internal temperature of −80° C. or lower, and themixture was stirred for 30 minutes. 1.39 mL of dichlorodihexylsilane wasadded dropwise thereto at an internal temperature of −80° C. or lower,and the mixture was maintained for one hour at this temperature.Subsequently, the temperature was slowly increased to room temperature.After 12 hours, 50 mL of a saturated aqueous solution of sodium hydrogencarbonate and 50 mL of ethyl acetate were added to the mixture, and theresulting mixture was left to stand to remove an aqueous layer. Theorganic layer was washed with water and saturated brine, and was driedover anhydrous magnesium sulfate, and then the solvent was distilled offThe residue thus obtained was purified by silica gel columnchromatography, and compound (1-B) was obtained. Yield amount: 1.6 g(yield: 47%).

1.35 g of compound (1-B) was dissolved in 27 mL of dry THF, and 0.73 gof N-bromosuccinimide was added thereto. A reaction liquid thus obtainedwas allowed to react for 4 hours at room temperature. The solvent wasdistilled off under reduced pressure, and the residue was purified bysilica gel column chromatography. Thus, compound (1-C) was obtained.Yield amount: 0.94 g (yield: 90%).

In a nitrogen atmosphere, 0.44 g of bis(1,5-cyclooctadiene)nickel(0),0.75 mL of 1,5-cyclooctadiene, and 0.27 g of 2,2′-bipyridyl weresuspended in 10 mL of N,N-dimethylformamide (DMF), and a solutionprepared by dissolving 0.71 g of compound (1-C) in 5 mL of DMF was addeddropwise to this suspension. The mixture was stirred for 24 hours at 60°C. A reaction liquid obtained was added dropwise to a mixed liquid of 5mL of 2 mol/L hydrochloric acid and 10 mL of methanol, and a solid thusobtained was washed with 2 mol/L hydrochloric acid, an aqueous solutionof disodium ethylenediamine tetraacetate, an aqueous solution of sodiumdiethyldithiocarbamate, and methanol. Subsequently, the solid wastransferred to a Soxhlet extractor and washed with acetone. The solidthus obtained was dried under reduced pressure, and thus a polymer 1 wasobtained. Yield amount: 0.47 g.

The polymer 1 was subjected to an analysis of molecular weight by GPC,and the weight average molecular weight (Mw) calculated relative tostandard polystyrenes was 22,000. The ratio of the weight averagemolecular weight to the number average molecular weight (Mw/Mn) was1.45. Furthermore, the polymer 1 was dissolved in chlorobenzene, and thesolution was applied on a glass substrate by spin coating. Theabsorption spectrum of the coating film was measured, and it was foundthat λmax was 670 nm. Meanwhile, measurement of the absorption spectrumwas carried out using a spectrophotometer (Model UV-3600 manufactured byShimadzu Corp.).

Example 2 Synthesis of Polymer 2

Compound 2-C was synthesized according to the following scheme, andpolymer 2 was synthesized from this compound 2-C.

Compound (2-B) was synthesized in the same manner as in Example 1,except that 1.39 mL of dichlorodihexylsilane was changed to 1.63 g ofdichlorodi(2-ethylhexyl)silane. 1.6 g (yield: 47%). Also,dichlorodi(2-ethylhexyl)silane was synthesized according to thesynthesis method for Compound 2 described in Journal of the AmericanChemical Society, Vol. 130, pp. 16144-16145 (2008).

Compound (2-C) was synthesized in the same manner as in Example 1,except that 1.35 g of compound (1-B) was changed to 1.46 g of compound(2-B). Yield amount: 1.1 g (yield: 95%).

Polymer 2 was synthesized in the same manner as in Example 1, exceptthat 0.71 g of compound (1-C) was changed to 0.79 g of compound (2-C).Yield amount: 0.50 g.

The polymer 2 was subjected to an analysis of molecular weight by GPC,and the weight average molecular weight (Mw) calculated relative tostandard polystyrenes was 21,000. The ratio of the weight averagemolecular weight to the number average molecular weight (Mw/Mn) was1.53. Similarly, the absorption spectrum of the coating film of polymer2 was measured, and it was found that λmax was 680 nm.

Example 3 Synthesis of Polymer 3

Compound 3-E was synthesized according to the following scheme, andpolymer 3 was synthesized from this compound 3-E.

Compound (3-B) was synthesized using compound (3-A) according to themethod described in Justus Liebigs Annalen der Chemie, Vol. 512, p.136-156 (1934). Compound (3-C) was synthesized by making reference tothe method described in Journal of Heterocyclic Chemistry, Vol. 20, p.113-119 (1983). Compound (3-D) was synthesized by making reference tothe method described in Journal of Heterocyclic Chemistry, Vol. 20, p.113-119 (1983). Compound (3-E) was synthesized by making reference tothe method described in Bioscience, Biotechnology, Biochemistry, Vol.57, 1561-1562 (1993).

Polymer 3 was synthesized in the same manner as in Example 1, exceptthat 0.71 g of compound (1-C) was changed to 0.48 g of compound (3-E).Yield amount: 0.24 g.

The polymer 3 was subjected to an analysis of molecular weight by GPC,and the weight average molecular weight (Mw) calculated relative tostandard polystyrenes was 17,000. The ratio of the weight averagemolecular weight to the number average molecular weight (Mw/Mn) was1.51. Similarly, the absorption spectrum of the coating film of polymer3 was measured, and it was found that λmax was 630 nm.

Example 4 Synthesis of Polymer 4

According to the following scheme, polymer 4 was synthesized from thiscompound 4-A.

Compound (4-A) was synthesized using compound (3-E) by making referenceto the method described in Tetrahedron Letters, Vol. 47, 2009-2012(2006).

Polymer 4 was synthesized in the same manner as in Example 1, exceptthat 0.71 g of compound (1-C) was changed to 0.51 g of compound (4-A).Yield amount: 0.26 g.

The polymer 4 was subjected to an analysis of molecular weight by GPC,and the weight average molecular weight (Mw) calculated relative tostandard polystyrenes was 18,500. The ratio of the weight averagemolecular weight to the number average molecular weight (Mw/Mn) was1.47. Similarly, the absorption spectrum of the coating film of polymer4 was measured, and it was found that λmax was 630 nm.

Example 5 Synthesis of Polymer 5

According to the following scheme, polymer 5 was synthesized from thiscompound 5-A.

Compound (5-A) was synthesized using compound (3-E) by making referenceto the method described in Tetrahedron Letters, Vol. 47, 2009-2012(2006).

Polymer 5 was synthesized in the same manner as in Example 1, exceptthat 0.71 g of compound (1-C) was changed to 0.53 g of compound (5-A).Yield amount: 0.29 g.

The polymer 5 was subjected to an analysis of molecular weight by GPC,and the weight average molecular weight (Mw) calculated relative tostandard polystyrenes was 17,300. The ratio of the weight averagemolecular weight to the number average molecular weight (Mw/Mn) was1.43. Similarly, the absorption spectrum of the coating film of polymer5 was measured, and it was found that λmax was 620 nm.

Example 6 Synthesis of Polymer 6

According to the following scheme, polymer 6 was synthesized from thiscompound 6-D.

Compound (6-B) was synthesized using compound (6-A) according to themethod described in Journal of Organic Chemistry, Vol. 62, p. 4088-4096(1997). Compound (6-C) was synthesized by making reference to themethods described in Helvetica Chimica Acta, Vol. 85, p. 4485-4517(2002) and Collection of Czachoslovak ChemicalCommunications, Vol. 51,p. 1678-1684 (1986). Compound (6-D) was synthesized by making referenceto the method described in Bioscience, Biotechnology, Biochemistry,1993, Vol. 57, p. 1561-1562.

Polymer 6 was synthesized in the same manner as in Example 1, exceptthat 0.71 g of compound (1-C) was changed to 0.46 g of compound (6-D).Yield amount: 0.23 g.

The polymer 6 was subjected to an analysis of molecular weight by GPC,and the weight average molecular weight (Mw) calculated relative tostandard polystyrenes was 16,500. The ratio of the weight averagemolecular weight to the number average molecular weight (Mw/Mn) was1.54. Similarly, the absorption spectrum of the coating film of polymer2 was measured, and it was found that λmax was 710 nm.

Example 7 Synthesis of Polymer 7

Polymer 7 was synthesized as follow.

0.12 g of compound (1-C), 0.15 g of compound (7-A) (synthesized by themethod described in Example 1 of WO 2008/067023), 2.1 mg oftris(dibenzylideneacetone)dipalladium(0), 4.2 mg of triphenylphosphine,and 35 mg of Aliquat 336 were dissolved in 20 mL of toluene and 15 mL ofTHF, and 2 mL of a 2 mol/L aqueous solution of sodium carbonate wasadded thereto. The solution was degassed and then purged with nitrogen,and the solution was allowed to react for 48 hours at 90° C. Thereaction liquid thus obtained was cooled to room temperature, and thesolvent was distilled off under reduced pressure. The residue thusobtained was washed with methanol, and was washed with acetone. A solidthus obtained was dissolved in chloroform, the solution was filteredthrough a 0.45-μm filter, and the solvent was distilled off underreduced pressure. A solid thus obtained was dissolved in toluene, andthe solution was mixed with an aqueous solution of sodiumdiethyldithiocarbamate. The mixture was stirred for 12 hours at 80° C.in a nitrogen atmosphere. After the mixture was left to stand, theaqueous layer was removed, ion exchanged water was added to the organiclayer, and the resulting mixture was stirred. After the mixture was leftto stand, the aqueous solution was removed, and the organic layer wasrecovered. The organic layer was dried over anhydrous magnesium sulfate,and then the solvent was distilled off under reduced pressure. A solidthus obtained was transferred into a Soxhlet extractor, and the solidwas extracted with methanol for 12 hours and further extracted withacetone for 12 hours. The solid was dried under reduced pressure, andthus polymer 7 was obtained. Yield amount: 0.16 g.

The polymer 7 was subjected to an analysis of molecular weight by GPC,and the weight average molecular weight (Mw) calculated relative tostandard polystyrenes was 19,100. The ratio of the weight averagemolecular weight to the number average molecular weight (Mw/Mn) was1.42. Similarly, the absorption spectrum of the coating film of polymer7 was measured, and it was found that λmax was 640 nm.

Example 8 Synthesis of Polymer 8

Polymer 8 was synthesized as follow.

Polymer 8 was synthesized in the same manner as in Example 7, exceptthat 0.15 g of compound (7-A) was changed to 0.08 g of compound (8-A)(synthesized by the method described in Example 17 of WO 2003/074533).Yield amount: 0.10 g.

The polymer 8 was subjected to an analysis of molecular weight by GPC,and the weight average molecular weight (Mw) calculated relative tostandard polystyrenes was 23,100. The ratio of the weight averagemolecular weight to the number average molecular weight (Mw/Mn) was1.45. Similarly, the absorption spectrum of the coating film of polymer8 was measured, and it was found that λmax was 630 nm.

Example 9 Synthesis of Polymer 9

Polymer 9 was synthesized as follow.

0.26 g of compound (1-C) and 0.35 g of compound (9-A) (synthesized bythe method described in Example 1 of JP-T-2010-507233) were dissolved in12 mL of dehydrated toluene, and 12.55 mg oftris(dibenzylideneacetone)dipalladium(0) and 28.80 mg oftriphenylphosphine were added. The solution was degassed and then purgedwith nitrogen, and was allowed to react for 48 hours at 120° C. Thereaction liquid thus obtained was cooled to room temperature, and thesolvent was distilled off under reduced pressure. The residue thusobtained was washed with methanol, and was washed with acetone. A solidthus obtained was dissolved in chloroform, the solution was filteredthrough a 0.45-μm filter, and the solvent was distilled off underreduced pressure. A solid thus obtained was dissolved in toluene, thesolution was mixed with an aqueous solution of sodiumdiethyldithiocarbamate, and the mixture was stirred for 12 hours at 80°C. in a nitrogen atmosphere. After the mixture was left to stand, theaqueous layer was removed, ion exchanged water was added to the organiclayer, and the resulting mixture was stirred. After the mixture was leftto stand, the aqueous solution was removed, and the organic layer wasrecovered. The organic layer was dried over anhydrous magnesium sulfate,and then the solvent was distilled off under reduced pressure. A solidthus obtained was transferred into a Soxhlet extractor, and the solidwas extracted with methanol for 12 hours and extracted with acetone for12 hours. The solid was dried under reduced pressure, and thus polymer 9was obtained. Yield amount: 0.34 g.

The polymer 9 was subjected to an analysis of molecular weight by GPC,and the weight average molecular weight (Mw) calculated relative tostandard polystyrenes was 19,700. The ratio of the weight averagemolecular weight to the number average molecular weight (Mw/Mn) was1.48. Similarly, the absorption spectrum of the coating film of polymer9 was measured, and it was found that λmax was 620 nm.

Example 10 Synthesis of Polymer 10

Polymer 10 was synthesized as follow.

Polymer 10 was synthesized in the same manner as in Example 9, exceptthat 0.35 g of compound (9-A) was changed to 0.26 g of compound (10-A)(synthesized by the method described on page 14 of WO 2010/062948).Yield amount: 0.26 g.

The polymer 10 was subjected to an analysis of molecular weight by GPC,and the weight average molecular weight (Mw) calculated relative tostandard polystyrenes was 18,600. The ratio of the weight averagemolecular weight to the number average molecular weight (Mw/Mn) was1.39. Similarly, the absorption spectrum of the coating film of polymer10 was measured, and it was found that λmax was 510 nm.

Example 11 Synthesis of Polymer 11

Synthesis of monomer 11-13 was carried out in the same manner as inScheme 1 described below, and polymer 11 was synthesized from thismonomer 11-13.

(Synthesis of Intermediate 11-2)

111.3 g of Compound 1 and 38.1 g of thiourea were added to 250 ml ofethanol, and the mixture was heated to reflux for 2 hours. The reactionliquid was poured into ice water, and a 10% aqueous solution of sodiumhydroxide was added thereto until the reaction liquid turned weaklyalkaline. The mixture was extracted with ethyl acetate. The extract waswashed with a saturated aqueous solution of sodium hydrogen carbonateand saturated brine, and then was dried over anhydrous magnesiumsulfate. After filtration, the solvent was distilled off under reducedpressure, and the residue was crystallized from an ethyl acetate/hexanemixed solvent. Thus, 100.2 g of an intermediate 11-2 was obtained.Yield: 82.0%.

(Synthesis of Intermediate 11-3)

56.5 g of copper (II) chloride was added to 1 L of acetonitrile, and44.5 g of isoamyl nitrite was added thereto at room temperature. Thetemperature was increased to 30° C., and then 92.8 g of the intermediate11-2 was added thereto over one hour at 30° C. to 32° C. The temperaturewas increased to 40° C., and the mixture was allowed to react for 2hours. Subsequently, the reaction mixture was poured into water, andethyl acetate was added thereto. The mixture was filtered throughCelite, and then the filtrate was subjected to liquid-liquid partition.The organic layer was washed with an aqueous solution of sodium sulfiteand saturated brine, and then was dried over anhydrous magnesiumsulfate. After filtration, the solvent was distilled under reducedpressure, and the residue was purified by silica gel columnchromatography. Thus, 71.8 g of an intermediate 11-3 was obtained.Yield: 71.7%.

(Synthesis of Intermediate 11-4)

Under water cooling, 22.1 g of the intermediate 11-3, 12.3 g ofn-octanethiol, and 23.1 g of potassium carbonate were added to 250 ml ofacetone, and the mixture was allowed to react for 6 hours at roomtemperature. The reaction mixture was poured into ice water, and ethylacetate and 5 ml of an aqueous solution of sodium hypochlorite wereadded thereto. The mixture was subjected to liquid-liquid partition, andthe organic layer was washed with saturated brine, and then was driedover anhydrous magnesium sulfate. After filtration, the solvent wasdistilled off under reduced pressure, and thus 30.6 g of an intermediate11-4 was obtained. Yield: 97.7%.

(Synthesis of Intermediate 11-5)

4.56 g of lithium aluminum hydride was added to 300 ml of dry THF, andwhile the mixture was cooled with an ice-acetone coolant, a solutionprepared by dissolving 29.9 g of the intermediate 11-4 in 100 ml of dryTHF was added dropwise thereto over 45 minutes at or below 5° C. Themixture was allowed to react for 15 minutes at or below 5° C., and then50 ml of acetone was added dropwise thereto over 5 minutes at or below17° C. The mixture was stirred for 10 minutes at room temperature, andthen 50 ml of 1 N aqueous hydrochloric acid was added dropwise theretoover 15 minutes under water cooling. The mixture was stirred for 30minutes at room temperature, and then ethyl acetate and hexane wereadded thereto. The mixture was filtered through Celite, and then thefiltrate was subjected to liquid-liquid partition. The organic layer waswashed with water, a saturated aqueous solution of sodium hydrogencarbonate, and saturated brine, and then was dried over anhydrousmagnesium sulfate. After filtration, the solvent was distilled off underreduced pressure, and the residue was purified by silica gel columnchromatography. Thus, 19.1 g of an intermediate 11-5 was obtained.Yield: 82.3%.

(Synthesis of Intermediate 11-6)

17.4 g of the intermediate 11-5 and 1.5 ml of pyridine were added to 200ml of toluene, and while the mixture was cooled with an ice-acetonecoolant, a solution prepared by dissolving 13.1 ml of thionyl chloridein 100 ml of toluene was added dropwise to the mixture over 25 minutesat or below 4° C. The mixture was allowed to react for one hour at orbelow 7° C., and then the reaction mixture was poured into ice water.The mixture was extracted with ethyl acetate. The mixture was subjectedto liquid-liquid partition, and the organic layer was washed with asaturated aqueous solution of sodium hydrogen carbonate and saturatedbrine, and then was dried over anhydrous magnesium sulfate. Afterfiltration, the solvent was distilled off under reduced pressure, andthus 18.2 g of an intermediate 11-6 was obtained. Yield: 92.8%.

(Synthesis of Intermediate 11-7)

16.3 g of the intermediate 11-6 and 50 ml of 1 N aqueous hydrochloricacid were added to 200 ml of acetone, and the mixture was heated toreflux for 3 hours. Furthermore, 20 ml of 1 N aqueous hydrochloric acidwas added to the mixture, and the resulting mixture was heated to refluxfor 5.5 hours. The mixture was extracted with ethyl acetate, and theorganic layer was washed with a saturated aqueous solution of sodiumhydrogen carbonate and saturated brine, and then was dried overanhydrous magnesium sulfate. After filtration, the solvent was distilledoff under reduced pressure, and thus 15.4 g of an intermediate 11-7 wasobtained. Yield: 100%.

(Synthesis of Intermediate 11-8)

15.1 g of the intermediate 11-7 and 6.3 g of sodium thioacetate wereadded to 200 ml of acetone, and the mixture was stirred for one hour atroom temperature. The mixture was poured into water, and the mixture wasextracted with ethyl acetate. The mixture was subjected to liquid-liquidpartition, and the organic layer was washed with a saturated aqueoussolution of sodium hydrogen carbonate and saturated brine, and then wasdried over anhydrous magnesium sulfate. After filtration, the solventwas distilled off under reduced pressure, and the residue was purifiedby silica gel column chromatography. Thus, 14.9 g of an intermediate11-8 was obtained. Yield: 87.5%.

(Synthesis of Intermediate 11-9)

13.9 g of the intermediate 11-8 and 1.0 ml of pyridine were added to 150ml of toluene, and while the mixture was cooled with an ice-acetonecoolant, a solution prepared by dissolving 4.4 ml of thionyl chloride in50 ml of toluene was added dropwise to the mixture over 30 minutes at orbelow 5° C. The mixture was allowed to react for one hour at or below 5°C., and then the reaction mixture was poured into ice water. The mixturewas extracted with ethyl acetate. The mixture was subjected toliquid-liquid partition, and the organic layer was washed with asaturated aqueous solution of sodium hydrogen carbonate and saturatedbrine, and then was dried over anhydrous magnesium sulfate. Afterfiltration, the solvent was distilled off under reduced pressure, andthus 14.1 g of an intermediate 11-9 was obtained. Yield: 96.5%.

(Synthesis of Intermediate 11-10)

13.2 g of the intermediate 11-9 was added to 200 ml of acetone, andwhile the mixture was cooled with an ice-acetone coolant, 7.4 ml of a28% sodium methoxide methanol solution was added dropwise thereto over10 minutes at or below 0° C. under nitrogen stream. The mixture wasstirred for 30 minutes at or below 5° C., and then was poured intowater. The resulting mixture was extracted with ethyl acetate. Theresulting mixture was subjected to liquid-liquid partition, and theorganic layer was washed with a saturated aqueous solution of sodiumhydrogen carbonate and saturated brine, and then was dried overanhydrous magnesium sulfate. After filtration, the solvent was distilledoff under reduced pressure, and the residue was purified by silica gelcolumn chromatography. Thus, 8.53 g of an intermediate 11-10 wasobtained.

Yield: 82.3%.

(Synthesis of Intermediate 11-11)

8.04 g of the intermediate 11-10 was added to 100 ml of toluene, and6.81 g of DDQ was added thereto over 10 minutes at room temperature. Themixture was heated to reflux for 2 hours, and then was poured into icewater. The mixture was extracted with ethyl acetate. The mixture wassubjected to liquid-liquid partition, and the organic layer was washedwith an aqueous solution of sodium sulfite, a saturated aqueous solutionof sodium hydrogen carbonate, and saturated brine, and then was driedover anhydrous magnesium sulfate. After filtration, the solvent wasdistilled off under reduced pressure, and the residue was purified bysilica gel column chromatography. Thus, 6.56 g of an intermediate 11-11was obtained. Yield: 82.2%.

(Synthesis of Intermediate 11-12)

5.75 g of the intermediate 11-11 was added to 100 ml of chloroform, and7.59 g of m-CPBA was added thereto over 30 minutes under ice cooling.The temperature was increased to room temperature, and the mixture wasstirred for 3 hours. The mixture was poured into ice water, and wasextracted with chloroform. The mixture was subjected to liquid-liquidpartition, and the organic layer was washed with an aqueous solution ofsodium sulfite, a saturated aqueous solution of sodium hydrogencarbonate, and saturated brine, and then was dried over anhydrousmagnesium sulfate. After filtration, the solvent was distilled off underreduced pressure, and the residue was purified by silica gel columnchromatography. Thus, 4.87 g of an intermediate 11-12 was obtained.Yield: 76.7%.

(Synthesis of Intermediate 11-13)

4.76 g of the intermediate 11-12 was added to 100 ml of chloroform, and5.87 g of N-bromosuccinimide was added thereto over 30 minutes under icecooling. The temperature was increased to room temperature, and themixture was stirred for one hour. Subsequently, the mixture was pouredinto ice water, and the resulting mixture was extracted with chloroform.The resulting mixture was subjected to liquid-liquid partition, and theorganic layer was washed with a saturated aqueous solution of sodiumhydrogen carbonate and saturated brine, and then was dried overanhydrous magnesium sulfate. After filtration, the solvent was distilledoff under reduced pressure, and the residue was purified by silica gelcolumn chromatography. Thus, 6.54 g of an intermediate 11-13 wasobtained. Yield: 91.8%.

(Synthesis of Polymer 11)

Compound (11-A) was synthesized using compound (1-C) by making referenceto Example 1 of US Patent Application No. 2008/0121281 A1.

Polymer 11 was synthesized in the same manner as in Example 7, exceptthat 0.12 g of compound (1-C) was changed to 0.11 g of intermediate11-13, and 0.15 g of compound (7-A) was changed to 0.10 g of compound(11-A). Yield amount: 0.10 g.

The polymer 11 was subjected to an analysis of molecular weight by GPC,and the weight average molecular weight (Mw) calculated relative tostandard polystyrenes was 20,300. The ratio of the weight averagemolecular weight to the number average molecular weight (Mw/Mn) was1.47. Similarly, the absorption spectrum of the coating film of polymer11 was measured, and it was found that λmax was 690 nm.

Example 12 Synthesis of Polymer 12

Polymer 12 was synthesized as follow.

Compound (12-B) was synthesized using compound 12-A (synthesized by themethod described in the specification of US Patent Application No.2009/0326187 A1) according to a method known.

Polymer 12 was synthesized in the same manner as in Example 7, exceptthat 0.15 g of compound (7-A) was changed to 0.11 g of compound (12-B).Yield amount: 0.10 g.

The polymer 12 was subjected to an analysis of molecular weight by GPC,and the weight average molecular weight (Mw) calculated relative tostandard polystyrenes was 19,500. The ratio of the weight averagemolecular weight to the number average molecular weight (Mw/Mn) was1.49. Similarly, the absorption spectrum of the coating film of polymer12 was measured, and it was found that λmax was 680 nm.

Here, polymer 1 is an example polymer A-1; polymer 2 is an examplepolymer A-6; polymer 3 is an example polymer A-16; polymer 4 is anexample polymer A-23; polymer 5 is an example polymer A-17; polymer 6 isan example polymer A-24; polymer 7 is an example polymer B-9; polymer 8is ais an example polymer B-1; polymer 9 is an example polymer B-11;polymer 10 is an example polymer B-12; polymer 11 is an example polymer10; and polymer 12 is an example polymer B-9.

(Synthesis of Comparative Polymers)

Comparative polymers A to D were synthesized as follow.

(Synthesis of Comparative Polymer A)

The following comparative polymer A of cyclopentadithiazole wassynthesized by the method described in WO 2008/067023 (p. 12-13).

The comparative polymer A was subjected to an analysis of molecularweight by GPC, and the weight average molecular weight (Mw) calculatedrelative to standard polystyrenes was 18,300. The ratio of the weightaverage molecular weight to the number average molecular weight (Mw/Mn)was 1.44. Similarly, the absorption spectrum of the coating film ofcomparative polymer A was measured, and it was found that λmax was 660nm.

(Synthesis of Comparative Polymer B)

The following comparative polymer B was synthesized by the methoddescribed in Example 1 of JP-T-2010-507233.

The comparative polymer B was subjected to an analysis of molecularweight by GPC, and the weight average molecular weight (Mw) calculatedrelative to standard polystyrenes was 22,000. The ratio of the weightaverage molecular weight to the number average molecular weight (Mw/Mn)was 1.47. Similarly, the absorption spectrum of the coating film ofcomparative polymer B was measured, and it was found that λmax was 580nm.

(Synthesis of Comparative Co-Polymer C)

Comparative co-polymer C having a structure described in the right sidewas synthesized by the method described in WO 2008/067023 (p. 12-13).

The comparative co-polymer C was subjected to an analysis of molecularweight by GPC, and the weight average molecular weight (Mw) calculatedrelative to standard polystyrenes was 21,600. The ratio of the weightaverage molecular weight to the number average molecular weight (Mw/Mn)was 1.43. Similarly, the absorption spectrum of the coating film ofcomparative polymer B was measured, and it was found that λmax was 660nm.

(Synthesis of Comparative Co-Polymer D)

Comparative co-polymer D having a structure described in the right sidewas synthesized by the method described in Example 3 ofJP-T-2010-507233.

The comparative co-polymer D was subjected to an analysis of molecularweight by GPC, and the weight average molecular weight (Mw) calculatedrelative to standard polystyrenes was 19,100. The ratio of the weightaverage molecular weight to the number average molecular weight (Mw/Mn)was 1.38. Similarly, the absorption spectrum of the coating film ofcomparative polymer B was measured, and it was found that λmax was 570nm.

(Production of Photovoltaic Cell)

Photovoltaic cells were formed on glass ITO substrates by the followingprocedure, using polymers 1 to 12 and comparative polymers A to D.

On a clean, UV-ozone-treated ITO glass substrate, a PEDOT:PSS (CleviosPVP AI4083 of H.C. Stark GmbH) layer to be used as a hole transport layerwas spin-coated and dried for 15 minutes at 120° C.

Subsequently, a mixture (mass ratio 1:1) of one of the p-typesemiconductor polymers synthesized as the polymers 1 to 12 andcomparative polymers A to D, and PC61BM ([60]PCBM manufactured bySolenne BV) was dissolved in o-dichlorobenzene, and then the solutionwas spin coated on the PEDOT:PSS layer and dried for 15 minutes at 120°C. Thus, a photoelectric conversion layer was formed.

Furthermore, a dehydrated ethanol solution (2 mass %) of titaniumisopropoxide (manufactured by Sigma-Aldrich Co.) was spin coated on thisphotoelectric conversion layer, and the solution was dried for one hourat room temperature. Thus, an electron transport layer of a titaniumoxide layer was formed.

Thereafter, an upper electrode was formed by high vacuum deposition ofaluminum, and thereby a photovoltaic element was obtained.

At this time, two kinds of elements, namely a 2-mm square element and a20-mm square element, were produced by changing the size of the glassITO substrate used, and the pattern size of the ITO and depositedaluminum.

(Evaluation of Photovoltaic Cell)

1) Current Density-Voltage (J-V) Characteristics of Element

The 2-mm square element and the 20-mm square element respectivelyproduced as described above were subjected to a performance evaluationas follows.

For the elements thus obtained, the current density-voltage (J-V)characteristics of the elements were evaluated using a SMU2400 type I-Vmeasuring apparatus manufactured by Keithley Instruments, Inc. in anitrogen atmosphere (oxygen concentration: 1 ppm or less, moistureconcentration: 1 ppm or less). Filtered xenon lamp light from a solarsimulator manufactured by Oriel (Oriel) Instruments Corp. was used, andan AM1.5G spectrum of 100 mW/cm² was approximated. The short circuitcurrent (Jsc), open circuit voltage (Voc), fill factor (FF) and powergeneration efficiency (η) obtained in the apparatus are presented in thefollowing Table 1.

2) Retention Ratio of Power Generation Efficiency Exposed to Atmosphere

The 2-mm square element obtained as described above was exposed to thelight-shielded atmosphere (23° C., 50% RH) for 72 hours, and thereafter,the current density-voltage (J-V) characteristics of the element wereevaluated in the same manner as in the above section 1).

These results are presented in the following Table 1.

TABLE 1 photoelectric 2-mm square element 20-mm square conversion 2-mmsquare element (after exposure to Element layer, (inicial) theatmosphere) (inicial) Sample polymer λmax Jsc Voc FF η η Retention ηRetention No. examples [nm] [mA/cm²] [V] [%] [%] [%] ratio [%] [%] ratio[%] Remarks 1 polymer 1 670 10.3 0.70 54 3.9 3.3 85 3.4 87 Thisinvention 2 polymer 2 680 10.5 0.70 55 4.0 3.4 84 3.6 89 This invention3 polymer 3 630 9.8 0.69 54 3.7 3.1 85 3.0 82 This invention 4 polymer 4630 9.2 0.74 53 3.6 3.2 89 3.0 83 This invention 5 polymer 5 620 9.10.76 55 3.8 3.5 92 3.3 87 This invention 6 polymer 6 710 9.8 0.70 53 3.63.1 85 3.1 85 This invention 7 polymer 7 640 10.7 0.68 54 3.9 3.3 84 3.384 This invention 8 polymer 8 630 10.5 0.70 50 3.7 3.1 84 3.0 82 Thisinvention 9 polymer 9 620 10.6 0.69 52 3.8 3.1 82 3.4 89 This invention10 polymer 10 510 9.5 0.71 54 3.6 2.9 80 2.9 80 This invention 11polymer 11 690 11.6 0.70 55 4.5 3.9 87 3.9 87 This invention 12 polymer12 680 10.9 0.70 54 4.1 3.5 85 3.4 83 This invention 13 comparative 6609.7 0.68 48 3.2 2.2 69 2.1 66 Comparative polymer A example 14comparative 580 9.1 0.66 50 3.0 2.0 67 2.0 67 Comparative polymer Bexample 15 comparative 660 9.5 0.67 52 3.3 2.1 63 2.3 69 Comparativeco-polymer C example 16 comparative 570 10.0 0.64 50 3.2 1.5 47 1.8 56Comparative co-polymer D example

As a result, it can be seen that a solar cell elements using the organicsemiconductor polymers of the present invention have high powergeneration efficiency η, which have a high retention ratio of the powergeneration efficiency after exposure to the atmosphere, and in which thedecrease in the power generation efficiency is small when the elementsize is increased.

On the other hand, it can be seen that a solar cell elements using theorganic semiconductor polymers of Comparative Example have lowconversion efficiency η, in which the conversion efficiency η afterexposure to the atmosphere is prone to decrease, and in which thedecrease in the power generation efficiency is large when the elementsize is increased.

Having described our invention as related to the present embodiments, itis our intention that the invention not be limited by any of the detailsof the description, unless otherwise specified, but rather be construedbroadly within its spirit and scope as set out in the accompanyingclaims.

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2011-080999 filed in Japan on Mar. 31,2011, which is entirely herein incorporated by reference.

1. An organic semiconductor polymer having a structural unit representedby the following Formula (I):

wherein X represents Si, S or O; R¹ represents a hydrogen atom, an alkylgroup, a cycloalkyl group, an aryl group, an aromatic heterocyclic groupor an oxygen atom; p represents 0, 1 or 2; herein, the bond between Xand R¹ is such that when X is Si, the bond is a single bond, and when Xis S, the bond is a double bond. Furthermore, when X is O, p represents0, and when p is 2, two R¹'s may be the same or different from eachother, or two R¹'s may bond with each other to form a ring.
 2. Theorganic semiconductor polymer according to claim 1, wherein thestructural unit represented by Formula (I) is a structural unitrepresented by Formula (I-1):

wherein R¹′ and R¹″ each independently represent a hydrogen atom, analkyl group, a cycloalkyl group, an aryl group or an aromaticheterocyclic group; and R¹′ and R¹″ may bond with each other to form aring.
 3. The organic semiconductor polymer according to claim 1, whereinthe structural unit represented by Formula (I) is a structural unitrepresented by Formula (I-2):

wherein p′ represents 0, 1 or
 2. 4. The organic semiconductor polymeraccording to claim 1, wherein the structural unit represented by Formula(I) is a structural unit represented by Formula (I-3):


5. The organic semiconductor polymer according to claim 1, wherein theorganic semiconductor polymer is a co-polymer.
 6. The organicsemiconductor polymer according to claim 1, wherein the organicsemiconductor polymer is a co-polymer which further includes astructural unit represented by the following Formula (II):

wherein Z¹ and Z² each independently represent S, O, Se or Te; Yrepresents C(R²¹) or N; R and R²¹ each independently represent ahydrogen atom or a substituent.
 7. A composition for organicsemiconductor material, including the organic semiconductor polymeraccording to claim 1 and an n-type organic semiconductor molecule. 8.The composition for organic semiconductor material according to claim 7,wherein the n-type organic semiconductor molecule is fullerene or aderivative thereof.
 9. The composition for organic semiconductormaterial according to claim 8, wherein the fullerene or a derivativethereof is a phenyl-C₆₁-butyric acid ester, a diphenyl-C₆₂-bis(butyricacid ester), a phenyl-C₇₁-butyric acid ester, a phenyl-C₈₅-butyric acidester, or a thienyl-C₆₁-butyric acid ester.
 10. A photovoltaic cellincluding the organic semiconductor polymer or the composition fororganic semiconductor material according to claim
 1. 11. A photovoltaiccell including a layer containing the organic semiconductor polymer orthe composition for organic semiconductor material according to claim 1,between a first electrode and a second electrode.
 12. The photovoltaiccell according to claim 11, including a hole transport layer between thefirst electrode and the layer containing the organic semiconductorpolymer or the composition for organic semiconductor material.
 13. Thephotovoltaic cell according to claim 11, including an electron transportlayer between the second electrode and the layer containing the organicsemiconductor polymer or the composition for organic semiconductormaterial.
 14. The photovoltaic cell according to claim 11, wherein thefirst electrode is a transparent electrode.
 15. The photovoltaic cellaccording to claim 11, wherein the second electrode is a metalelectrode.
 16. A polymer having a structural unit represented by thefollowing Formula (I):

wherein X represents Si, S or O; R¹ represents a hydrogen atom, an alkylgroup, a cycloalkyl group, an aryl group, an aromatic heterocyclic groupor an oxygen atom; p represents 0, 1 or 2; herein, the bond between Xand R¹ is such that when X is Si, the bond is a single bond, and when Xis S, the bond is a double bond. Furthermore, when X is O, p represents0, and when p is 2, two R¹'s may be the same or different from eachother, or two R¹'s may bond with each other to form a ring.
 17. Thepolymer according to claim 16, wherein the structural unit representedby Formula (I) is a structural unit represented by Formula (I-1):

wherein R¹′ and R¹″ each independently represent a hydrogen atom, analkyl group, a cycloalkyl group, an aryl group or an aromaticheterocyclic group; and R¹′ and R¹″ may bond with each other to form aring.
 18. The polymer according to claim 16, wherein the structural unitrepresented by Formula (I) is a structural unit represented by Formula(I-2):

wherein p′ represents 0, 1 or
 2. 19. The polymer according to claim 16,wherein the structural unit represented by Formula (I) is a structuralunit represented by Formula (I-3):


20. The polymer according to claim 16, wherein the polymer is aco-polymer.
 21. The polymer according to claim 16, wherein the polymeris a co-polymer which further includes a structural unit represented bythe following Formula (II):

wherein Z¹ and Z² each independently represent S, O, Se or Te; Yrepresents C(R²¹) or N; R and R²¹ each independently represent ahydrogen atom or a substituent.